Patent GB-1328719-A (GB)
Title: Machine tools
IPC: B24B5/04
Filed: 1971-07-29
Abstract: 1328719 Grinding TOYODA KOKI KK 29 July 1971 [31 July 1970] 35695/71 Heading B3D A machine tool, such as a machine for grinding crank-shafts, comprises a support 3, 4 for a workpiece W, a support 9 for a tool 10, means for effecting relative movement between the supports, first timer means operable to be timed out after a predetermined time period from the start of a machining cycle for setting a constant machining cycle, a second timer means operable to be timed out after a predetermined time period from the start of a machining cycle for setting at least one check point during a machining cycle, means for detecting a difference between a predetermined machining cycle and an actual machining cycle at the check point, feed compensation means for effecting a correction of the speed of relative movement between the supports, and control means responsive to the detecting means for operating the compensating means to compensate for a difference between the predetermined and actual machining cycles. As described, the machine is for grinding the pins of a crankshaft W which is mounted between pot chucks 5, 6 on stocks 3, 4 carried by a table 2. The chucks can be rotated to angularly index the workpiece, and the table is longitudinally indexable to positions determined by a pin 8 engaging notche s in a plate 7. The grinding wheel 10 is movable transversely to the table by a feed mechanism and is driven by an electric motor. The feed mechanism consists of a lead screw 13 which engages a nut 12 on the support and a further nut 15 movable in a case 14 by fluid pressure supplied to a chamber 16 to eliminate backlash. One end of the lead screw is formed with a piston 17 slidable in a cylinder having its opposite ends connected by conduits 21, 23 to a valve 101, conduit 23 having a throttle 24. A shaft 31 extends from the piston through a spool valve 26 which can be axially moved by a dog 32 to close a line 28 from cylinder 18 to the valve 101. A splined shaft 35 is formed on the other end of the feed screw and engages a sleeve 36 in a gear 37 engaged, through a gear 38, with a gear 39 on a shaft 34 which is connected by a clutch 41, 42 to a handwheel 45 and a gear 40 meshing with a rack 51 on the rod of a piston 50 in a cylinder 52. One end of the cylinder is connected to a throttle valve 55, and a second throttle valve 56 controlled by valve 104 to a valve 107 which is also connected to the opposite end of the cylinder the valve 107 being connected to a further valve 102. The first end of the cylinder is also connected by a line 71 to a valve 105 and the speed compensating means 62 having valve spools V 1 , V 2 , V 3 . The valves 101, 102, 105 are connected to a pump 89 which is also connected to a valve 103 controlling a device 85, 86 for advancing a sizing device 84, the output of which passes through an amplifier 88a to a control device 88 which generates signals CH1, CH2, G1, CH3, CH4, G2. In operation, the workpiece is clamped in the pot chucks 5, 6 and when a start button is pressed, timers TR1, TR2, TR3, TR4 (Fig. 3, not shown) are actuated to time out at respective points K 1 , K 2 , K 3 , K 4  after respective times t 1 , t 2 , t 3 , t 4 . An electric circuit retracts valve 101 so that fluid is supplied to chamber 19 of cylinder 18 to advance the grinding wheel from point a to b at a rapid speed until dog 32 retracts valve spool 26 so that exhaust from the cylinder is only through throttle 24 for rapid feed of the grinding wheel during grinding of a shoulder of the workpiece from point c until the dog 33 actuates limit switch 252 at point d whereupon fluid is supplied through valves 102, 107 to the chamber 58 of cylinder 52. Fluid from chamber 53 of the cylinder passes through throttle 55 and valves 104, 107 and 102 to a tank, the piston rotating the feed screw through the rack 51 and shaft 39 at a rough grinding speed determined by the throttle. The fluid from chamber 53 also passes to chamber 67 of the spool valve V 1  and then to chambers 75 and 81 of spool valves V 2 , V 3 . If a limit switch LS3 is actuated by a dog 42a on the clutch 42 before timing out of time TR 1  at point K 1 , the grinding operation is proceeding normally. If the switch has not been actuated, valve 105 is actuated so that fluid from chamber 53 is supported to the right hand chambers 68, 76, 79 of valves V 1 , V 2 , V 3  and the fluid in the left hand chambers passes to the tank to increase the speed of the piston 50 and hence the feed. Pressure switches PS1, PS2 are actuated to operate valve 105 so that the valve spools V 1 , V 2 , V 3  are reciprocated until switch LS3 is actuated and rough grinding continues at a speed determined by throttle 55 and valve 103 is actuated to advance the sizing device 84. At point f the pin portion of the workpiece is commenced. After a time t 2 , timer TR2 times out at check point K 2 . If the signal from the sizing device and control device indicates that rough grinding is far from normal, valve 106 is again operated so that the valves V 1 , V 2 , V 3  are again reciprocated four times as counted by operation of switch PS2 to effect compensation. If there is only a small error in the time, valve 107 is actuated so that only valves V 1 , V 2  are reciprocated three times. When signal G1 is generated by control device 88 at point g valve 104 is actuated so that fluid from chamber 53 of cylinder 52 is exhausted through throttles 55 and 56 for a fine grinding speed. Timer TR3 times out at check point K 3  after a time t 3 . If grinding is not proceeding normally, control device 88 does not emit a signal and valve 105 is actuated and the valves V 1 , V 2 , V 3  are reciprocated twice to compensate for an error. If only a small error occurs in the time, the device 88 emits a signal CH3 and valves 105, 106 are actuated and the valve spools V 1 , V 2  reciprocated once. When the second sizing signal G2 is produced, valve 107 is actuated to stop the feed for a spark-out operation until timer TR4 times out at point K 4  after time t 4  and the grinding wheel is then retracted to its initial position i. Thereafter, the workpiece is angularly and longitudinally indexed for grinding the next pin. In another embodiment, the compensating means 62 consisting of valves V 1 , V 2 , V 3  and the throttle valves 55, 56 and valve 104 are replaced by a pair of valves in parallel in the exhaust line from cylinder 52, each valve having a spool axially adjustable by a stepping motor to vary its throttling effect, one valve controlling rough grinding and the other fine grinding.