Patent GB-797503-A (GB)
Title: Improvements relating to automatic control systems especially for machine tools
Inventor: SPENCER ROLF EDMUND
IPC: H03M1/80
Filed: 1953-10-21
Abstract: 797,503. Programming for machine-tools. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Oct. 8, 1954 [Oct. 21, 1953; Nov. 19, 1953; Nov. 19, 1953], Nos. 29126/53, 32055/53 and 32056/53. Class 83 (3). [Also in Group XXXVIII] In a continuous positional-control-system in which the controlling- variable is available in digital form, e.g. as digital numbers on a perforated or magnetic tape, interpolating means are used for translating the higher digits of the controlling- variable into a - coarse - analog - controlsignal. A fine analogue control signal is also similarly produced from the lower digits of the control signal and may be used directly or recorded as a phase, frequency or amplitude-modulated signal for subsequent control. For direct control, two fine-control signals are derived which differ in the value of the highest digit they represent, and are switched into the control-circuit alternately as the controlled shaft moves through a predetermined position, in order to prevent indeterminacy of the fine-control at the predetermined position. First embodiment, Figs. 1, 2. The controlled shaft 1, which may position the table of a milling-machine through a nut 3, is driven by a servomotor 2 and drives a coarse balancing potentiometer 12 at one one-hundred-andtwenty-eighth of, and the fine potentiometer 33 at one-half of, its speed. The control signal numbers, Fig. 2, shown at 5a in decimal form, are recorded in binary form in two parts 6, 7, the first (coarse) part 6 being the first eight binary digits of the number and the second (fine) part 7 the last eight digits of the binary number. Alternating voltages corresponding to the coarse digits are applied in succession, in groups of three, to an interpolator 8, which transposed them, as disclosed in Specification 796,994, [Group XXXVI], into analog D.C. signals which are compared at 10 with the voltage derived from the coarse potentiometer 12, the difference (error) signal operating the motor 2 until there is no significant output from the comparator 10 when a switch 20 is operated in known manner, e.g. by the coarse signal amplitude, to the position shown, to connect the fine error signal in the motor control circuit. Two interpolators 30, 31, similar to interpolator 8, produce fine analogue control signals, but they differ in that the highest binary digital value is added in one fine signal but subtracted from the other. The two fine signals are switched in alternately by a relay 40 as the shaft 1 passes a predetermined (zero) position, the relay at the same time connecting a corresponding one of diametral wipers 34-35 of the fine potentiometer to the comparator 11 so that the motor is brought to the balance position without any indeterminacy at the zero position. Second embodiment, Fig. 5. Coarse control and switch-over to fine control, are effected as in Fig. 1. The fine control signal, after translation into analogue form, is recorded on a magnetic tape 65 as phase-modulation of a signal wave relative to a reference wave. The reference wave, recorded along track 64, is picked off at 61, amplified at 69 and fed in quadrature to the stator windings of a syncroresolver 66. The phase-modulated signal wave recorded along track 63 is picked off at 60 and fed, with the output 70 of the resolver-stator, to a phase-discriminator 71, the D.C. output of which effects fine control of the motor. The fine control analogue signal may be recorded by a servo-system, similar to Fig. 1 but without the coarse control, in which the shaft 1 drives a synchro-resolver, the output of which is the phase-modulated signal wave. Modification. Amplitude- or frequencymodulation may be used alternatively, for recording the fine signal on the track 63. The coarse control signal may also be pre-recorded if desired. A number of machines may be controlled from one record. Work may be inspected by sensing it with a feeler whose instantaneous-position is converted into a corresponding electrical signal which is compared with the output of the apparatus above described, the comparator output, i.e. the work error, being recorded or operating an alarm. Specification 796,993, [Group XXXVIII], also is referred to.