Patent GB-1396061-A (GB)
Title: Control circuits
IPC: B23Q35/18
Filed: 1973-06-08
Abstract: 1396061 Copy turning S R CUDNOHUFSKY 8 June 1973 [12 June 1972] 27366/73 Heading B3T [Also in Divisions G3 and F2] A tracer control circuit for governing the operation of a pair of feed cylinders 18, 26 arranged to feed a cutting tool 32 in angularly related directions comprises a high pressure pump 36 connected to a tracer valve 10 which is variably restricted by the action of a stylus 12 engaging pattern 166, the pressure created by the restriction being supplied to cylinder 18, while cylinder 26 is supplied by a low pressure pump 34, the drain lines of cylinders 18, 26 being connected to a stability valve 112 which responds substantially solely to the rate of flow from the cylinders and which directs the flow to a sump via flow control valves 132 or 134. The latter can be selectively opened by solenoid valves 136 or 138 to permit a maximum flow to sump of 1 or 2 gals./min. respectively which thus determines the feed rate of cutting tool 32. The circuit includes solenoid controlled, pilot operated spool valves 40, 42, 44 which in the position shown are set for normal machining operation, e.g. of a lathe wherein cylinders 18, 26 control cross-slide 16 and carriage 20 respectively. Stability valve 112 includes a port 120 connected via lines 83, 86, 122 and valve 42 to the head side of cylinder 18, a port 124 connected via lines 102, 126 and valve 44 to the head side of cylinder 26, and a port 128 connected via valves 132 or 134 to sump. A spool 118 is slidably mounted in bore 116 and based towards port 124 by spring 119, a projection 146 on the spool pre. venting complete closure of port 124. A pin 150 engaging axial slot 148 prevents rotation of spool 118. A groove 152 in the latter registers with port 128 at all times and communicates with both ends of the spool so that the pressures thereat are substantially equal. Groove 152 has portions 154, 156 of uniform and tapering crosssection respectively, arranged such that spool 118 is moved away from port 124 solely in response to the rate of flow through port 128 as determined by the setting of valves 132 and 134. The position of spool 118 shown is that corresponding to a flow through port 128 of 1 gal./ min. and is maintained regardless of the pressure at ports 120, 124. Opposite groove 152 spool 118 is provided with an inclined flat surface 160 co-operating with bore 116 to define a tapered passageway 162 communicating with port 120. Passageway 162 is sized so that with given pressures at ports 120 and 124 the pressure drop through the passageway will be substantially constant regardless of the rate of flow through port 128. Thus smooth operation of the tracer is ensured irrespective of the feed rates of cylinders 18, 26, or of any change in oil viscosity. The solenoid valves 136, 138 can be actuated by limit switches which are tripped as the carriage reaches predetermined positions where the diameter of the workpiece changes, thus enabling approximately the same surface speed to be maintained. When the machining operation is completed a retract switch is manually or automatically actuated to shift the spool of valve 40 into a position (Fig. 6, not shown) in which pilot pressure in line 92 shifts the spool of valve 90 to directly connect the head ends of cylinders 18, 26. Simultaneously solenoid valve 136 is actuated to block the flow through valve 132 to sump. Thus oil from both pumps 34, 36 is directed to the rod end of cylinder 18 to retract stylus 12, the oil discharging from head end of cylinder 18 flowing to the head end of cylinder 26 to retract carriage 20. The oil in the rod end of cylinder 26 is discharged directly to sump 52 without passing through stability valve 112. The retraction stroke is relatively rapid compared with the feed stroke. Limit switches may be provided which operate such that if cross-slide 16 engages its limit switch first then valve 42 is moved into a position (Fig. 1, not shown) in which all the oil from pumps 34, 36 is directed to carriage cylinder 26. Similarly if carriage 20 engages its limit switch first then valve 44 is moved to a position (Fig. 1) in which all the oil is directed to cross-slide cylinder 18.