Patent GB-723871-A (GB)
Title: Fluid pressure power mechanisms
Inventor: JOHNSON CLARENCE
IPC: F15B11/044
Filed: 1951-03-28
Abstract: 723,871. Dashpots. ROCKWELL MANUFACTURING CO. March 28,1951, No. 7171/51. Class 108 (3). [Also in Group XXII] A power mechanism for effecting the relative advance and retract movements of a workpiece and a tool holder 28 &c., comprises a power member 8 advanced by fluid under pressure, applied at one side of the member, at a rate controlled by the flow of liquid in a closed circuit between the other side of the member and one side of a floating withdrawal piston 77 in a control cylinder 78, the other side of the withdrawal piston being subjected to fluid under pressure to effect retract movements, and a floating abutment piston 83 in the control cylinder, the withdrawal piston being moved away from the abutment piston by fluid under pressure admitted between them during retraction, while during advance, the withdrawal piston is first moved rapidly into engagement with the abutment piston and then at a slower rate depending on the operation of means controlling the rate of movement of the abutment piston whereby the power member may be moved through successive cycles each including a partial slow feed, a rapid retract and a rapid advance movement. The drill-chuck 28 is moved rapidly up to the work when pneumatic pressure is applied to the system at 106. Expulsion of liquid by the piston 8, as it advances, causes a piston 80 to be moved against a stop 82. When the piston 80 abuts the stop, the increase in pressure of the liquid expelled by the piston 8 moves pistons 77, 83 in unison to the left expelling liquid through passages 91 and 89, an adjustable orifice 96, passages 92 and 100 to a piston 102. The size of the orifice 96 thus determines the feed-rate of the drill. When it is desired to withdraw the drill, a valve 110 is moved to supply air pressure to the left side of the piston 102 and through the hollow rod of the piston 83 to a chamber 84. The drill is thus withdrawn rapidly until the piston 77 abuts the end of its cylinder. As the piston 80 remains against its stop, the drill is withdrawn only to a point just clear of the hole. Meanwhile, the piston 83 is moved slowly to the right by liquid passing through a ball-valve 94, having a weaker control spring 98 than a second ball-valve 93 which remains closed. The position reached by the piston 83 is determined by the time that the valve 110 is open and can be controlled by adjusting the orifice 95 of the valve 94. Thus, the drill will be returned to a point just short of that previously reached, when the valve 110 is reversed, before the feedrate again becomes effective. When the hole has been drilled to the depth determined by a stop 18, both valves 109 and 110 are moved to their right-hand positions. The drill is then rapidly withdrawn as the piston 80 is moved to its left-hand position, at which time the valve 93 opens to allow rapid movement of the pistons to their initial positions. The reservoirs of liquid behind the pistons 80 and 102 allow a considerable liquid loss without the operation of the system being affected. The circuit may be modified by replacing the piston 102 with a floating piston with no rod or a bellows &c. and by placing a pressure-reducing valve in the line 85.