Patent GB-572108-A (GB)
Title: Improvements in control systems for the reproduction of pattern contours
IPC: B23Q35/128
Filed: 1943-09-18
Abstract: 572,108. Photo-electric control of copying-machines. ARMSTRONG, J. J. V. (Linde Air Products Co.). Sept. 18, 1943, No. 15345. [Class 40 (iii)] [Also in Groups XXII, XXIII and XXXV] In a machine for producing a copy of a pattern, the tool, which may be a cutting torch, milling cutter, abrasive wheel &c. and a tracer are movable together relatively to the work and pattern along the line of the pattern, and transverse periodic movements are given to the tracer to carry it alternately on and off the pattern line, the length of these transverse movements being used to determine the resultant direction of movement of the tool so as to cause it to follow the required path along the pattern line. The machine comprises a slide 9 carrying the tool 1 and tracer 7 movable on transverse ways 11 on a table 12 which is movable along longitudinal guides 13 on the machine frame 14. The work W and pattern table 6 are mounted on fixed supports attached to the machine frame. Hydraulic cylinders 15, 16 are fixed to the machine frame and table 12 respectively so that combinations of the movements of the pistons therein will feed the tool in any compass direction, the fluid supply to the cylinders from a motor-driven gear pump being controlled by two rotary valves 31, 32, Fig. 16, coupled by rigid connecting rods 55, 56 to an eccentric 52 carried by a shaft 51, Fig. 7, rotatable by a gear 50. The speed of operation may be varied by byepassing part of the pump output to exhaust. The arrangement is such that, as shown in Fig. 16, a supply port 28 in. valve 32 is connected to the lower end of cylinder 16 whilst the upper end is connected to an exhaust line 38 and both ends of cylinder 15 are cut off from supply, thus causing the tool to be fed in a North direction at its maximum speed parallel to the arrow shown on the gear 50. Rotation of the gear and eccentric clockwise from this position will reduce the supply to cylinder 16 and open the left-hand end of cylinder 15 to supply, causing a combination of East and North feeds to be given to the tool, each at reduced speed, producing a resultant always parallel to the arrow, and when the latter is pointing due East the supply to cylinder 16 will be cut off and cylinder 15 will be traversing the tool East at its maximum speed. Other combinations of supply to the two cylinders produce a resultant feed in any required direction parallel to the arrow. The gear 50 is adapted to be rotated from an electric motor 78 through a belt 77, gearing 79, 80, Fig. 4, and either of the oppositely-rotating worms 84, 85. The gearing is carried by a parallel motion linkage 87, 89 which may be swung to cause either worm to engage the gear 50 by means of a shaft 96 attached to one of the links and an armature 95 lying between the poles of two electromagnets 91, 92. The tracer casing 7, Fig. 7, is carried by an arm 60 attached to the link 61 of a parallel motion linkage 61, 62, 64 whereof the link 61 engages an eccentric 66 on the lower end of the shaft 51 attached to the gear 50, the arrangement being such that normally, when the tracer is out of contact with the pattern, the worm 85 is engaged to rotate the gear 50 clockwise as seen in Figs. 4 and 16, the tracer also being given a clockwise orbital movement by the eccentric 66 so that its axis describes a small circle 70 whose radius is equal to that of the eccentric 66. In one form of tracer, a narrow pencil of light 3, focused by lenses 71 from a source 73, is directed through the lower end of the tracer casing 7 on to a transparent pattern plate 4 provided with an opaque pattern line 2, the light passing through the plate falling on a photo-sensitive device 5, preferably of the selenium cell type. The current variations produced in the cell 5 are amplified in a thermionic valve amplifier to control the solenoids 91, 92 so that when the major portion of the light pencil 3 reaches the cell, the solenoid 92 is energized to engage the worm 85. The clockwise motion of the pencil on the circle 70 will cause the pencil to overlap the pattern line 2 until sufficient light has been cut off from the cell 5 to de-energize the solenoid 92 and energize 91, whereupon the rotation of the gear 50 will be reversed and the pencil 3 will move laterally away from the pattern line until sufficient light again reaches the cell to reverse the rotation of the gear 50. If the pattern line is straight these lateral movements to and from the pattern will be short and will not cause any change in the setting of the valves 31, 32, so that the North feed will continue without interruption but if the line leads away to the right as at A, Fig. 16, the pencil will have to make a longer lateral movement before reversal takes place and consequently the gear 50 will be rotated clockwise sufficiently to affect the setting of the valves and cause a combined North and East feed to operate. As the line continues to bend away the gear 50 is further rotated clockwise until the feed becomes entirely East to follow the straight portion B of the pattern. In another form the tracer may consist of a resilient conductor projecting axially from the casing 7 to contact laterally with a conducting pattern and thus form a switch to energize one of the solenoids 91, 92, the other being energized by an opposing spring, or the tracer may consist of a yielding arm coacting with a non-conducting pattern to operate two contacts of a switch controlling both solenoids. The eccentric 66 for giving the orbital movement to the tracer is angularly adjustable on its shaft 51 so that, to produce work which is exactly the same size as the pattern, the radius of maximum eccentricity is set in line with the arrow of resultant motion, as shown in Fig. 16, whereas, if work slightly larger than the pattern is required in order to allow a subsequent machining operation to be performed, the eccentric 66 is displaced by an amount 145, Fig. 25, from the arrow so that the centre 70<1> of the orbital movement 70 will always lie outside the pattern line 2, and the work will be larger than the pattern by this amount. Similarly, to mill work identical in size with the pattern, the eccentric 66 is displaced by an amount 145 equal to the radius of the milling cutter 143 so that the axis of rotation of the cutter will follow the centre 70<1> of the orbital path. For milling cutters of larger diameter, the eccentric 66 is replaced by one of greater throw to increase the width of the orbital path and enable a larger adjustment 145 to be made. The extent of the lateral periodic movements which must take place before reversal of the gear 50 occurs may be adjusted by altering the sensitivity of the valve amplifier through grid potential rheostats. A circuit for the amplifier, which is fed by a multiple voltage transformer, is described. Specification 561,171 is referred to.