Patent GB-1090057-A (GB)
Title: Spool valve, in particular for a tracer system for machine tools
IPC: B23Q35/18
Filed: 1964-11-27
Abstract: 1,090,057. Copy-milling. A. JENSON. Nov. 27, 1964, No. 48402/64, Heading B3K. A spool valve, having means for balancing pressures occasioned by leakage, comprises a valve spool 30 having first, second, third and fourth lands mutually spaced, and a casing with which said lands are in bearing contact, said casing including a first port 181 with which the first land 180 is normally in register, a hydraulic liquid pressure supply connection 82 opening to the casing between the first land and the second land 81, said casing having a second port 80 with which the second land is normally in register, the width of the second port slightly exceeding the width of the second land, a pressure liquid discharge connection 83 communicating with the casing between the second land and the third land, a liquid return connection 95 communicating with the casing between the third land 96 and the fourth land 66, said casing further having a port 97 with which the fourth land is normally in register and which is slightly wider than the fourth land, and a liquid exhaust connection 68 opening through the casing beyond the fourth land, and means 188 providing a by-pass connection from the first mentioned port to the liquid return connection 95, which together with-an orifice 185 through the first land constitutes the means for balancing pressures occasioned by leakage, and in use, prevents motor creep. In a copy-milling machine having a table, cross-saddle and knee, the valve 30 is oscillated by a motor 31, an eccentric 32 and a lever (35) to overcome static friction. It is urged axially to the right by a spring (37). A rod 36, Fig. 6, of the valve is urged against a lever 47 acted upon by the tracer valve stem 20 which can oscillate or move axially. Should excessive movement of the tracer occur, a screw 56 rocks a lever 54 to actuate a switch 52 and stop the machine. The right-hand part of the valve 30 controls the knee and the left-hand part controls either a saddle for cross-movement or a work-table for longitudinal movement. A manual control valve 75 enables knee movement to be reversed and a similar further manual control valve 90 determines whether scanning shall be effected by table or by saddle movement. In the central position of the valve 30, Fig. 9, when the knee movement is zero, a clearance exists between a land 81 and a duct 80. Fluid flows via a scan-reversing valve 85 to, in this instance, the table motor 27. The exhaust passes via a similar clearance between a land 66 and a duct 97. If the valve is moved further to the left, the knee motor is operated to move the knee downwardly. The valve 85 is actuated by a solenoid controlled by switches and limit dogs to reverse the scanning movement according to the member being moved-in this case, the table. At the same time, a time switch 153 momentarily actuates a valve 125 to give an increment of feed to the saddle; a throttle valve 151 meanwhile creates a back pressure to actuate a valve 129 and cut off power to the motor 27 driving the table. Any two motors can be controlled for copying, with the third providing an incremental feed.