Patent GB-793957-A (GB)
Title: Automatic surface grinding
IPC: B24B49/18
Filed: 1955-05-03
Abstract: 793,957. Surface grinding; trueing wheels. JONES & SHIPMAN, Ltd., A. A., and HOULDSWORTH, J. Aug. 1, 1956 [May 3, 1955], No. 12805/55. Class 60. Relates to a surface grinding machine in which a workpiece is ground in strips by relatively stepping the worktable 27, Fig. 1, and grinding wheel 39 in the transverse direction at each end of each of a series of relative longitudinal strokes between the members until the entire area to be ground is covered, continuing the operation with the direction of the transverse steps reversed so as to re-grind the area in the opposite sense, and so on, an increment of down feed being applied to the grinding wheel at each reversal of the sense or pattern of the grinding. According to the invention, the machine operates in a first rough-grinding phase, second wheel-trueing phase, and third finish-grinding phase and is provided with stop means to arrest automatically the relative movement at the end of the first phase, means to reciprocate a trueing device relatively to the wheel with a down feed of the latter during the second phase, means to stop the third phase after a pre-determined amount of finish grinding, and means for automatically starting the second and third phases at the end of the preceding phase. The worktable 27, Figs. 1 and 8, is reciprocated longitudinally by the ram of a hydraulic cylinder 37 on a saddle 28 which is movable in transverse steps on the machine bed 78, by' the ram of a hydraulic cylinder 38 ; adjustable dogs 53 co-operate with a trip lever 54 for actuating a valve 51 to set the table for reversal at each end of its stroke and similar dogs act on valves 52, 66 to provide for the reversal of the saddle at each end of a complete series of transverse steps of the saddle. The table 27, in addition to carrying a magnetic chuck MC for the workpiece, supports a holder 42 for a trueing diamond 32 ; this holder is arranged to be reciprocated on the table by a motor M, Fig. 7, which drives a feed screw 96 and is automatically reversed at each end of its stroke by adjustable dogs 43 actuating a reversing switch LS6. The grinding wheel, Fig. 1, is vertically movable on a pillar 40 by a screw 1, Fig. 3, which is screw-threaded in the pillar and rotated through gearing 2 by a shaft 3. This shaft can be rotated in either direction by a hand wheel 4 or hydraulic motor 5 so as to move the head in either direction and incrementally for effecting down feed in the two grinding phases by a fluid-operated piston 11, Fig. 5, in a cylinder 10, the piston operating a ratchet-andpawl feed 7, 8 and being returned by a spring 12; the increment of down feed is set by adjustable nuts 13 coacting with the frame 14 and such increment may be reduced for the finishgrinding phase by energising a solenoid SOL11 to pivot a stop 17 into the path of the nuts 13. Stops 19, 24, 22, Fig. 3, on a rotatably-adjustable disc 25 co-operate with a stop 20, pivoted link 23 and pin 21 on the hand wheel 4 for, respectively, setting the grinding head in its initial position, at its limit of down feed for the first phase, and, after withdrawal of the link 23 by the energisation of a solenoid SOL10, at its limit of down feed for the third phase. For the trueing phase which follows automatically on the first phase, the disc 25 is given an increment of rotation by gearing 35, 36 through a pawl-and-ratchet 33, 34 actuated by the temporary energization of a solenoid SOL9 whereby the stop 24 is moved away from the stop 23, and energization of a solenoid valve SOL8, Fig. 8, activates the hydraulic motor 5 until the stops 23, 24 again engage. The stops 19, 24, 22 are adjustably mounted on the disc 25 so that they can be correctly positioned when setting up the machine and for the initial trueing of the grinding wheel. The cylinders 37, 38 actuating the table and saddle, and the motor 5 and cylinder 10 actuating the grinder, are included in a hydraulic circuit as shown in Fig. 8 which is arranged for automatic operation under the control of electric solenoids, relays and switches appropriately actuated in the machine cycle. At the start of a working cycle with the table 27 positioned " full right" in Fig. 1 and the saddle 28 " full outward," fluid is directed through gate valves 56, 57 and SOL3 to move the table leftwards until dogs 53 thereon actuate the valve 51 which is then set to permit the passage of fluid to reverse a valve 58 and the associated valve 56. Since the valve 57 is unaffected, the table stops, but fluid from the valve 58 moves rightwards a combined valve 59, 60 with the result that fluid passes temporarily through the centre cage C of the valve 60 and valves 64, 65 and SOL5 to the cylinder 38 so as to give the saddle an increment of inward movement, the rate of which depends upon the speed of the valve 60 as set by a throttle 67. At the end of this movement, the valve 59 directs fluid through a valve 68 and valve 52 to reverse the valve 57 and so permit flow to the cylinder 37 to return the table to its initial position until the dogs 53 again actuate the valve 51 and, by causing reversal of the combined valve 59, 60, provide for a further inward movement of the saddle followed by reverse movement of the table. This sequence of movements continues until, when the whole area of the workpiece has been traversed, dogs on the saddle actuate combined valves 52, 66, whereby fluid is directed to the valve 65 to reverse it and bring the saddle to a stop, the table being already halted ; at this stage, one corner of the working area is under the grinder head. A valve 70 which moves with the valve 65 then acts to reverse pressure conditions in a combined valve 71, 68, 72 so that the valve 71 in its movement permits a temporary flow of fluid to the cylinder 10 to apply an increment of down feed to the grinder. At the end of this movement of the combined valve, the valve 68 directs fluid to reverse the valve 57 so that the table resumes its traverse and, since the valve 72 similarly reverses the valve 64, the saddle is again advanced in steps, but in the outward direction instead of inward as before so as to reverse the grinding pattern. Another increment of down feed is applied to the grinder head when the saddle again reaches its outward limit of travel, and the sequence is continued until the stops 23, 24, Fig. 3, in the down feed mechanism engage. Switches are then effective to set the circuit so that the grinding continues for a further traverse over the entire workpiece area until, at the end of this operation, the movement of the valve 71 results in insufficient fluid pressure being supplied to the cylinder 10 to overcome the action of the stops 23, 24 ; the solenoid valve SOL3 is then reversed with the result that the table moves to its extreme right position and, by actuating a limit switch LS1, results in the movement of the solenoid valve SOL5 to traverse the saddle to its extreme outward position where it actuates a switch LS2 signalling that the diamond 32 is now correctly positioned under the grinder. The solenoid SOL9, Fig. 3, is then energized to rotate the disc 25 to position the stop 24 away from the stop 23 a distance setting the limit of down feed for trueing, and a switch LS3, Fig. 3, actuated by the solenoid, sets the circuit so that the solenoid valve SOL8, Fig. 8, activates the hydraulic motor 5 for down feed. The diamond 32 is then reciprocated across the wheel by operation of the motor M, Fig. 7, an increment of down feed being applied by the motor 5 at each end of each traverse, under the control of a ratchet-and-pawl counter 47, 74, Fig. 10, which is set forward one step for each traverse of the diamond by the energization of a solenoid SOL7 until, after a pre-set number of traverses a finger 75 on the ratchet 47 actuates a limit switch LS7 to prevent further down feed and stop the motor M after the diamond has completed its traverse. Traverse of the table and saddle is then resumed, together with the increments of down feed of the grinder by the cylinder 10, for the third and last phase of the operation ; the link 23 is also withdrawn from its stop 24 by energizing the solenoid SOL10, Fig. 3, and the solenoid SOL11, Fig. 5, is energized if it is desired to use the stop 17 to reduce the increments of down feed. When the stops 21, 22 come into contact during the final increment of down feed, the control circuit provides for more than one further coverage of the workpiece area to allow for " sparking out" ; the table and saddle therefore continue their traverse under the cotnrol of a ratchet-and-pawl counter 48, 76, Fig. 10, which is set forward one step by the energization of a solenoid SOL6 for each workpiece coverage after the last increment of down feed until, after a pre-set number of such coverages, a finger 77 on the ratchet 48 actuates a switch LS8. The hydraulic motor 5 then raises the grinder to its initial position, the table and saddle are restored to their initial outer positions, and the counters 47, 48 are zeroised by their springs 49, 50. The control circuit is so arranged that, should the table, saddle and grinder be in intermediate positions when the hydraulic circuit is first activated by its pump, these members are automatically moved to their initial positions and then stopped, and the machine cannot be started on a cycle unless the members are all in their start positions. The machine may incorporate a gauge 80, Fig. 18, for checking the size of the workpiece at the end of the first phase of operation and before trueing, and, if it discloses that the workpiece has not been sufficiently ground down, provides for the setting of the control circuit to apply the necessary further down feed to the grinder and resumption of traverse of the table and saddle. The feeler arm of the gauge is pivoted on a vertical pivot 81 adjacent the work area and caused by the automatic energization of a solenoid SOL 13 to swing from i