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An automatic tensioning system for a chain drive system of a rock drill assembly is disclosed. A hydraulic cylinder is coupled to one end of the feed channel of a rock drill assembly. When pressurized hydraulic fluid is provided to the hydraulic cylinder, a plunger within the hydraulic cylinder pull

An automatic tensioning system for a chain drive system of a rock drill assembly is disclosed. A hydraulic cylinder is coupled to one end of the feed channel of a rock drill assembly. When pressurized hydraulic fluid is provided to the hydraulic cylinder, a plunger within the hydraulic cylinder pulls on a tensioner sprocket, which in turn provides tension to the chain of the chain drive system. This allows for a constant tension to be applied to the chain throughout a long duration of operation as opposed to a manually adjusted chain drive system in which the chain tension varies during operation in between manual adjustments.

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1. A rock drill assembly, comprising: a feed channel having a guide rail;a rock drill configured to translate along the guide rail;a tensioner member movably coupled to the feed channel;a chain feed drive fixedly coupled to the feed channel and having a drive sprocket;a chain attached to the rock dr

1. A rock drill assembly, comprising: a feed channel having a guide rail;a rock drill configured to translate along the guide rail;a tensioner member movably coupled to the feed channel;a chain feed drive fixedly coupled to the feed channel and having a drive sprocket;a chain attached to the rock drill and engaging the tensioner member and the drive sprocket;an actuator associated with the tensioner member and configured to apply a substantially constant tensioning force to the tensioner member to tension the chain, the actuator comprising a through-bore hydraulic cylinder with a plunger and a hydraulic fluid inlet port; anda rod coupled to the tensioner member and extending through the through-bore hydraulic cylinder;so that when pressurized hydraulic fluid is provided to the through-bore hydraulic cylinder, the force on the plunger is transmitted to the rod thereby tensioning the chain. 2. The assembly of claim 1, further comprising: a check valve coupled to the hydraulic fluid inlet port; and a hydraulic line coupled to the check valve. 3. The assembly of claim 2, further comprising: an adjusting nut disposed on an end of the rod extending through the through-bore hydraulic cylinder. 4. The assembly of claim 1, further comprising: a mark on the feed channel and a mark on the tensioning member, such that the marks being roughly coincident indicates that the chain has stretched. 5. The assembly of claim 4, wherein the indication signifies that the chain should be replaced. 6. The assembly of claim 1, further comprising: a switch coupled to the feed channel and actuatable by the tensioner member to provide an indication of chain stretch exceeding a predetermined threshold. 7. The assembly of claim 1, wherein the tensioner member comprises a clevis and a tensioner sprocket, and the chain engages the tensioner sprocket. 8. The assembly of claim 1, further comprising: a drive idler sprocket coupled to one of the chain feed drive and the feed channel, wherein the chain further engages the drive idler sprocket. 9. The assembly of claim 1, wherein the chain has first and second ends that are attached to the rock drill such that the chain and the rock drill form a loop. 10. An automatic tensioning system for a chain-driven rock drill assembly, comprising: a guided clevis adapted to translate along a feed channel of the rock drill assembly;a tensioner sprocket coupled to the guided clevis;a through-bore hydraulic cylinder mounted on one end of the feed channel and having a plunger;a rod having a first end coupled to the guided clevis and a second end extending through the plunger; anda fastener coupled to the rod on the second end to prevent the rod from sliding through the plunger. 11. The tensioning system of claim 10 wherein the rod is a threaded rod and the fastener is an adjusting nut which engages with the threaded rod, and the system further comprises: a washer between the plunger and the adjusting nut, an outer diameter of the washer being greater than an inner diameter of the plunger so that force acting on the plunger is transmitted to the rod via the adjusting nut and washer. 12. The tensioning system of claim 10, wherein the chain-driven rock assembly has a chain which is engagable with the tensioner sprocket. 13. The tensioning system of claim 10, wherein the through-bore hydraulic cylinder includes: a hydraulic inlet port and the system further comprises a check valve coupled to the hydraulic inlet port. 14. The tensioning system of claim 13, further comprising: a hydraulic line coupled to the check valve through which pressurized hydraulic fluid is provided to the through-bore hydraulic cylinder. 15. The tensioning system of claim 10, further comprising: a hydraulic port in the through-bore hydraulic cylinder; a three-way valve coupled to the hydraulic inlet port; and a check valve coupled to the three-way valve. 16. The tensioning system of claim 15 wherein the three-way valve is manually operable to allow flow between the check valve and the hydraulic cylinder when the three-way valves is in a normal-operation position and to allow flow between the hydraulic cylinder and a bleed off line when the three-way valve is in a chain-replacement position. 17. A method for providing a rock drill assembly with an automatic tensioning system, comprising: sliding a piston of a through-bore hydraulic cylinder over a threaded rod coupled to a guided clevis, the guided clevis coupled to a tensioning sprocket;tightening an adjusting nut onto the threaded rod to snug up to the through-bore hydraulic cylinder; andcoupling a hydraulic supply line to an inlet of the through-bore hydraulic cylinder. 18. The method of claim 17 wherein the threaded rod is part of a manually-adjusted tensioning system and the method further comprises removing a nut from the threaded rod prior to sliding the through-bore hydraulic cylinder over the threaded rod. 19. The method of claim 17 further comprising: replacing a rod of a manually-adjusted tensioning system with the threaded rod prior to sliding the through-bore hydraulic cylinder over the threaded rod, the threaded rod being longer than the rod of the manually-adjusted tensioning system to accommodate length of the through-bore hydraulic cylinder. 20. The method of claim 19, further comprising: coupling a locking nut with the threaded rod to lock the adjusting nut.