Patent GB-698487-A (GB)
Title: Improvements in or relating to machine tools
IPC: B24B47/20
Filed: 1950-05-02
Abstract: 698,487. Machine-tool details. JONES & SHIPMAN, Ltd., A. A., and HOULDSWORTH, J. April 26, 1951 [May 2, 1950], No. 10791/50. Class 83 (iii). [Also in Group XXIII] A machine tool of the kind including a traversable work-table or carriage and a head adapted to support a tool, e.g. cutter or grinding wheel, and to be moved towards and away from the table or carriage by hydraulic means, has electrical means directly operable by the tool head in its travel to control the operation of the hydraulic means and thus the feed of the tool, and to determine the final extent of the tool feed. The table 2 carrying the rotating work W is longitudinally traversable on the machine framing 1; the tool head 3 carrying the grinding wheel G is transversely movable on the framing 1 by a feed screw 5 and nut 83. The screw 5 is rotated by a shaft 6 through gearing 7, 8, 9, 4; the shaft 6 carries a handwheel 16 for manual operation, and also carries a ratchet wheel 10. The ratchet wheel 10 co-operates with a spring-influenced pawl 11 pivoted on pin 13 in a carrier 12 mounted for swinging movement about the pin 13 which is carried by an arm 14 having a boss 15 loosely mounted for oscillatory movement relatively to the shaft 6. A tension spring 17 connected to the swinging pawl carrier 12 and to a fixed part tends to withdraw the pawl 11 from engagement with the ratchet teeth; the carrier 12 is connected by link 18 to a feed ram 19 operated by fluid pressure under the control of a relay valve 20 in turn controlled by a valve 21. A recess in the underside of the pawl-carrier receives with play a pin 24 projecting from the pawl-actuating arm 14. The extent of the operative strokes of the pawl is determined by front and back stops 25, 26 within the valve 21 and co-operating with the pin 24 which works in a slot in the valve; the back stop 26 is axially adjustable by a screw 28 or automatically by application of fluid pressure between the screw 28 and the back stop which has a slotted head 26a. The valve 21 carries, between lock nuts 29, 30, a stop plate 31 cooperating with pivoted spring-influenced catch levers 32, 33 shouldered for engagement, when permitted, behind the plate 31 to arrest the valve 21, thereby stopping the feed ram 19 and disengaging the pawl 10 from the ratchet wheel to stop the feed. The lever 32 which controls traverse feed has a tail portion 32a acted on by a screw 34 on a spring-controlled connection 35 actuated from the work table. At each end of each traverse of the work table, the connection is operated to lift the lever 32 clear of the plate 31, thus freeing the valve 21 which then operates to effect feed of the tool head 3 to the extent of one step, whereupon the lever 32 is permitted to return to its operative position to stop any further feed for the duration of the full traverse of the table. The catch lever 33 which controls plunge feed has an upturned portion 33a stepped for engagement with a trigger 36 having a nose 36a in the path of a cam 37 on the ratchet wheel 10 ; when the ratchet wheel moves to zero position at the termination of an operation the cam 37 acts on the trigger 36 and releases the catch lever 33 for engagement with the stop plate 31. To change over from traverse feeding to plunge feeding, the lever 32 is lifted clear of the stop plate 31 by a cam 38 actuated by a lever 39. To operate the feed mechanism in a fully automatic cycle, a manually settable lever 40 is positioned to engage the tail 33b of lever 33, so disengaging the lever 33 from the stop plate 31 and simultaneously closing electrical contacts 41, thereby energizing an electrical control unit 42 which in turn causes switches 43, 44 to take over the control of the complete hydraulic arrangement. The switches are affixed to the tool head and advance therewith during feed so as to approach a stop 45 adjustable by a micrometer. Switch 43 has an adjustable stop screw 43a in advance of a stop 44a on switch 44. Thus before the final position of the tool head is reached, the contacts of switch 43 are broken, this resulting in a solenoid 46 becoming energized by an electric relay in the control unit 42 ; the energized solenoid 46 operates a valve 47 whereby fluid pressure previously applied to feed ram 19 via a feed rate control screw 48 is now transferred to a slow feed rate control member 49 resulting in a reduction in the rate of feed during the final movement of the tool head 3. If the cam 38 is set to give an intermittent feed triggered by the movement of the work table, then a valve 50 on the shaft of cam 38 will allow fluid pressure to be applied to the bore of the valve 21 when valve 47 moves, thereby moving the back stop 26 in advance of the setting of screw 28, resulting in a reduction in magnitude of the feed as applied at each reversal of the work table. The switch 44 operates when the final position of the tool head is reached, causing the three following actions to take place simultaneously through the electric relay in control unit 42, viz:-(1) An electromagnetic brake or positive stop is applied to a stop disc 51 rigidly fixed to the feed shaft 6. This stop may be of the friction type consisting of a solenoid, the poles 52 of which form the brake shoes which are held in close proximity to the disc 51 by a swing arm 53 mounted for rotation about a fixed pin 54. Alternatively, a positive stop 55 comprises a segment of ratchet teeth in close proximity to the disc 51 which is also provided with ratchet teeth; the segment is carried by an arm 56 rotatable about a pin 57 by the action of a solenoid 58. (2) Energization of a solenoid 59 causes a valve 60 to move to a position such that the fluid pressure applied to the feed ram 19 is allowed to escape, at the same time the supply being discontinued. The pawl 11 is thus disengaged from the ratchet wheel 10 and no further feed is applied. (3) An electrical timing device (not shown) is set in motion, and this device, after a given time dependent upon the setting of the device, energizes a solenoid 61, thus disengaging a catch 62 from an interlock lever 63 so allowing a spring 65 to withdraw the lever 63 from a catch plate 64 secured to a master start lever 66 which is thereupon moved by a spring 67 to a position 66a. The circuit through the solenoid 61 is thus broken at contacts 68 thereby releasing the catch 62 which is now set for re-engagement with the interlock lever 63 by a spring 69. Movement of the master start lever to position 66a rotates, through link 71, a valve 70 to a position such that fluid pressure to the feed unit is further disconnected, i.e. no automatic feed is possible. Further, a valve 73 on the shaft of the master start lever is rotated to a position in which fluid is redirected to the opposite ends of cylinders 74, 75. A piston 76 in cylinder 74 is connected to a rack 76a engaging a pinion 77 freely rotatable on the shaft 6; rotation of the pinion 77 in reverse direction to normal feed movement causes a pawl 78 to engage a reset wheel 79, secured to shaft 6, under the action of a spring 80, a lever 81 connected to the pawl 78 being moved away from a fixed stop 82. Engagement of the pawl 78 causes shaft 6 to rotate with the pinion 77, this rotation continuing either until piston 76 completes its travel to the end of the cylinder or contacts on adjustable stop. The feed shaft 6 is thus reset to original position. When the application of fluid pressure to cylinder 75 is reversed, the tool head is moved away from the work, thus resetting switches 43, 44, de-energizing solenoids 46, 52 (or 58), 59, and disconnecting the supply to solenoid 61; the valves 47, 60 are reset by springs 84, 85. A link 86 connects the master start lever 66 to a lever 87 rotatable on a control shaft 88; a plunger 89 slidable in a control lever 90 can be manually engaged in the lever 87, resulting in complete control of the machine for traversing operation by the master start lever 66. A master stop 91 can be operated at any time during the cycle to disengage the catch 62 from the interlock lever 63 so as to reset the machine.