Patent ID: 8888416

Claim:
A control system for an air driven drill, wherein the control system is of the kind that includes, a cylinder having a feed piston positioned inside the cylinder, such that the feed piston defines a feed chamber within the cylinder, the feed chamber having a volume that is varied only by movement of the feed piston, a clamp piston positioned inside the cylinder, such that the clamp piston defines a clamp chamber within the cylinder, the clamp chamber having a volume that is varied only by movement of the clamp piston, wherein the feed piston and the clamp piston define a linking chamber between them, and the feed piston defines a one way valve that permits air in the feed chamber to flow one way into the linkage chamber, whereby the feed piston and the clamp piston move in unison in the cylinder during a feed stroke; a feed chamber line configured to supply compressed air to the feed chamber, and thereby configured to create an unbalanced force on the feed piston for moving the feed piston and thereby for applying the feed stroke to the drill, a clamp chamber line configured to sequentially introduce compressed air into the clamp chamber, and to vent compressed air from the clamp chamber through a vent hole in a feed valve; the control system being characterized in that it further comprises: an interrupt line that connects the feed chamber line to the clamp chamber line, so that compressed air fed via the feed chamber line to the feed chamber is also fed to the clamp chamber whereby the unbalanced force on the feed piston becomes balanced so as to stop the feed stroke; an adjustable frequency generator positioned in the interrupt line and configured to cause air flow downstream of the frequency generator to pulsate between a high pressure pulse and a low pressure pulse; whereby, during a feed stroke under which compressed air is fed to the feed chamber, compressed air fed to the clamp chamber via the interrupt line is caused by the adjustable frequency generator to pulsate, so that the feed stroke is caused to be stopped for a first period during a high pressure pulse, then resumed for a second period during a low pressure pulse, to cause a periodically interrupted feed stroke; wherein the interrupt line includes a connecting conduit extending between the adjustable frequency generator and the vent hole in the feed valve, whereby the interrupt line is configured to feed compressed air to the clamp chamber via the vent hole in the feed valve.