Patent GB-578883-A (GB)
Title: Improvements in or relating to milling and like machine tools
IPC: B23Q35/18
Filed: 1943-09-02
Abstract: 578,883. Fluid - pressure servomotor - control systems. STEVENS, A. H. (Cincinnati Milling Machine Co.). Sept. 2, 1943, No. 14354. [Class 135] [Also in Group XXII] In a milling or like copying machine for producing three dimensional work, a separate tracer is provided for controlling the motions in each of two mutually perpendicular planes. The machine comprises a bed 10 on which the work table 11 is movable longitudinally and a pillar 15 having transverse guides 16 for a carriage 17 on which the cutter slide 22 is movable vertically, these three perpendicular motions being actuated by fluid pressure cylinders 12, 18, 23, Figure 12, respectively: A pattern carrier 123 is mounted on the table 11 and a bracket 56 on the slide 22 carries a tracer housing 53 which is adjustable relatively to the cutter in three dimensions by means of perpendicular slides 57, 58 and 60. The tracer 61 in the housing 53 co-operates with a pattern 124, Figures 1 and 2, to control the cylinders 12, 18 in a horizontal plane by lateral contact with the pattern and a second tracer 175 on the slide 60 co-operates by end pressure with a depth pattern 176 to control the cylinder 23. The tracer 61, Fig. 3, is carried by a flexible diaphragm 62 clamped at the edges to the housing 53 and resting on an annular fixed rim 66 so that it can oscillate and move upwardly but not downwardly. The portion 71 of the tracer is surrounded by two yokes 80, 81 movable by lateral movement of the tracer in directions at right angles to each other to actuate valves 26, 42 for controlling the cylinders 12, 18 respectively. A spring- pressed plunger 114 in a sleeve 109 rotatably adjustable on a bracket 180 attached to the housing 53 acts on one side of the tracer to bias it in one direction and thus cause feeds of the table 11 and carriage 17 to take place when the tracer is out of contact with the pattern. The sleeve 109 is rotatable through ninety degrees within a collar 120 indexable on the bracket 108 to positions ninety degrees apart so that if the sleeve is set in one position to cause the feeds to move the tracer relatively to the pattern in a North and East direction, as shown by the arrows 128, 129 in Figure 2, the tracer will be maintained against an adjustable gauge bar 126 by the North feed and will traverse along the bar to the right by the East feed until it encounters the edge 130 of the pattern, whereupon both feeds will stop until the operator rotates the sleeve through ninety degrees to transfer the bias to the North and West feeds. The resultant direction of feed along the gauge 126 will then be reversed and by moving the gauge laterally by means of a hand-operated screw 133 a/ parallel cutting traverse in the opposite direction is performed until the opposite edge of the pattern is encountered by the tracer. Indexing the ring 120 alters the direction in which the resultant feed is biassed so that by successive indexings the tracer may follow round a closed pattern. The plungers 38, 50 of the valves 26, 42 are attached to the yokes 80, 81 to move therewith and control the supply of fluid from a pump 32 to opposite ends of the cylinders 12, 18 respectively, the supply also being led to plungers 88, 89 acting in opposite directions on the yokes so as to tend to restore the tracer to neutral position and prevent creeping. A sleeve 72 on the tracer is pressed by spring 75 into contact with an adjustable collar 100 thereon so that a tapered end 73 on the sleeve may engage a fixed ring 77 in the housing 53 to limit the oscillations of the tracer and hence the speed at which the cylinders 12, 18 act. This speed may be varied by adjustment of the collar 100 to vary the clearance between the taper 73 and the ring 77. The biassing plunger 114 may be held out of engagement with the tracer by a cross pin' 118 and the operator may then deflect the tracer by hand to cause it to follow round the pattern, always causing the two feeds to operate which will move the tracer towards the surface being followed and tangential to the surface, and a rapid feed in any direction may be effected by rocking a lever 106, Fig. 3, pivoted at 104 to the sleeve 72 and having knife edges engaging the top surface of the collar 100 so as to raise the conical end 73 of the sleeve and allow the tracer to be deflected by hand to a larger extent in the direction in which the rapid feed is required. The second tracer 175 is mounted by a ball joint 176<1> in its housing 136 and acts on a servo valve 188 through a ball 178, a spring 182 tending to maintain the valve in its lowest position in which fluid flows from the central supply port 183 by channel 191 to a selector valve 137, passing'into the interior of the spool 138 and acting against a fixed plunger 140 to force the spool to the right and cut off supply from the vertical cylinder 23. Deflection of the tracer upwardly reduces the pressure in pipe 191 so that a smaller pressure from the pipe 195 may act on the larger end of the spool 138 to move it to the left as shown in Fig. 12 so that fluid may flow by pipes 142, 148 to opposite ends of cylinder 23, the pressure acting on the larger lower surface of the piston 24 feeding the cylinder and slide 22 downwards to engage the tracer with the pattern 176 and the cutter with the work. The pattern then acts on the tracer during lateral movement by the cylinders 12, 18 to move the valve 136 to one side or the other of its mid position and thus vary the pressures on opposite sides of the piston 24 to feed the cutter and tracer upwardly or downwardly. A hand controlled servo valve 158 is also provided for the cylinder 23, the valve being mounted on the slide 22 and moved up or down by rotation of a screw 161 engaging a stationary nut segment 162 and rotatable in the slide 22 by a hand wheel 174, the screw having a splined connection with the driving member on the slide. With the tracer 175 out of contact with the pattern and the valve 136 therefor in its lowest position, the valve 138 is in the right hand position and raising or lowering of the valve 158 will allow fluid to flow from the supply line 34 and central port 154 to one end or the other of the valve and thence by pipe 146 or- 147 through valve 137 to upset the balance in the cylinder 23 and cause up or down feed of the cutter and tracer. Since the housing 135 of the valve 158 moves with the slide 22 whilst the serew 161 remains stationary when it is not being rotated the valve 158 will be restored to central position and the feed of the slide 22 will cease unless the screw is rotated continuously by hand. As soon as the tracer 175 engages the pattern the valve 138 will be moved to the left, cutting off the supply 34 from the valve 158 and, therefore, rendering the hand control ineffective. Movement of valve 138 to the left also admits fluid from supply 34 by port 197 to pipe 199 and cylinder 200 whose plunger 202 rocks the nut segment 162 about a pivot 164 to disengage it from the screw 161 and hence prevent damage to the valve 158 by continued rotation of the screw. If the operator should cause the tracer 61 to foul an object during downward feed of the slide 22 the upward movement of the tracer will raise a valve 208 and allow fluid to flow from the supply 34 by ports 211, 212 and pipes 213, 206 to the cylinder 200 to disengage the nut segment 162 and stop the downward feed, a resistance coil 205 preventing the supply from passing to the exhaust line 37 but allowing the spring 203 to discharge the cylinder 200 through the pipe 206 when returning the nut segment into engagement with the screw.