Patent GB-552415-A (GB)
Title: Improvements in and relating to electric controls for machine tools
IPC: B23Q35/123
Filed: 1941-01-08
Abstract: 552,415. Transformers. TRIGGS, W. W. (Niles-Bement-Pond Co.). Jan. 8, 1941, No. 289. [Class 38 (ii)] [Also in Groups XXXVIII and XL] In a machine for copying a model, the tracer incorporates a single electromagnetic unit which controls electric circuits for determining the speed of the cutter to and from the work in accordance with the slope of the path it follows. In a die-sinking machine in which the tracer and cutter perform successive traverses, the following and traversing motors are controlled concurrently to give a constant tangential speed over the model. The spindle 38 of the tracer 37, Fig. 3, is universally mounted within a barrel 32 which is free to slide within the casing 18 and is pressed forward by springs 35. The spindle has a ball-and-cone coupling with the armature 46 of a tilt detector 51-53, so that tilting of the tracer shifts the armature 46 against a spring 49 and in a manner described later, operates a solenoid 54 which by means of its armature 59 withdraws the barrel 32 and allows the spindle 38 to regain the central position. The tracer moves axially if the slope of its path is small and the movement is imparted to the barrel 32 directly through the spring 49. In either case, the movement of an armature 60 which is integral with the armature 59 and is separated therefrom by a non-magnetic spacer 63 affects the displacement detector 64-66 to control the motors. The tilt detector comprises a pair of excitation coils 51, 52, Fig. 4, fed with both A.C. and D.C., and a pick-up coil 53 connected in the grid circuit of a triode 78 which controls the solenoid 54. The A.C. bias is adjusted so that the triode is normally slightly conducting and that the voltage induced in the coil 53 by the movement of the armature 46 combines therewith in proper relationship. The displacement detector comprises a pair of excitation coils 64, 65, Fig. 6, fed with both A.C. and D.C. so that the voltage in the pick-up coil 66 is dependent on the rate of movement of the armature 60. The coil 66 is centre-tapped and controls a pair of pentodes 102, 103, which in turn control a pair of triodes 130, 131 supplying current to the two sets of brushes 148, 149 of the rotor of the following motor 23, which is of the reversible repulsion type. All the valves receive an A.C. bias, which in the case of the triodes is adjusted so that they are normally slightly conducting, and equal currents flow through both sets of brushes, the motor remaining stationary. When the armature 60 moves, a voltage dependent on the direction and rate of movement develops across the output terminals 122, 123 of the pentodes and causes an increase of current in one brush circuit and a decrease in the other, and the motor 23 therefore rotates at a corresponding speed. If the speeds of the following motor 23 and the traversing motor 14 are to be inter-related, the circuits shown in Fig. 5 are employed, and terminals 158, 159, Fig. 6, instead of being strapped together, may be connected to corresponding terminals in Fig. 5. The two motors rotate the multipole magnets 187, 202 of two pilot generators, the outputs of which are taken through potentiometers to 192, 208 full-wave rectifiers 195, 211 and applied to potentiometers 172, 173 in the grid circuit of a triode 169, which receives also both an A.C. and D.C. bias from potentiometers 175, 177. The traversing motor 14 is also of the repulsion type and its brush circuit receives from the triode 169 a voltage which is dependent on its own speed and on that of the following motor 23, and by suitable adjustment of the various potentiometers it may be arranged that the sum of the squares of the speeds is constant. The potentiometers 192 serves to regulate the maximum speed of the motor 14, and a second output from the pilot generator of the motor 23 is taken through a potentiometer 219 and rectifier 222 to regulate the speed of that motor by further biasing the triodes 130, 131. Instead of the tilt detector being of the form shown in Fig. 3, in which the excitation coils 51, 52 produce no flux in the armature 46, until it moves axially away from a central position, the form shown in Figs. 8, 9, 10 may be employed, in which a rotary armature 239 has two semi-cylindrical parts 240, 241 located between pole-pieces 244 carried by uprights 243, 245 at either end of a yoke 242. An excitation coil B surrounds the yoke 242, while a pick-up coil A surrounds the armature 239, so that a voltage is induced in the latter when the armature is rotated to bring the parts 240, 241 into unsymmetrical relation to the pole-pieces at either end. The coil B may be excited with A.C., but preferably a combination of A.C. and D.C. is used. Specification 544,209 is referred to.