Patent GB-1011078-A (GB)
Title: Apparatus for varying the resolution of interpolation of an interpolator
IPC: G05B19/18
Filed: 1963-02-08
Abstract: 1,011,078. Interpolating techniques. CINCINNATI MILLING MACHINE CO. Feb. 8, 1963 [Feb. 26, 1962], No. 34791/64. Divided out of 1,011,077. Heading G4G. An interpolating device used in an automatic control system for a machine tool (fully described in Specification 1,011,077, see Division G3) includes a number of interpolator stages, each stage being provided with more output terminals than input terminals, and the inputs being connected to the outputs by a plurality of impedance paths such as the winding spans of an autotransformer. The source providing the interpolator input signals, which represent values of a function at relatively widely spaced intervals of a variable of the function, is connected to the input terminals of the first stage, and switching arrangements are included between adjacent interpolator stages so that each terminal of a following stage may be connected to one of a set or group of output terminals of the preceding stage, the switching arrangements being operated by the cycling of a shift register. This arrangement enables the resolution of interpolation between any two interpolator input signals to be varied. In the described embodiment the interpolating device comprises three stages, each stage including a pair of bridge arrangements, the bridges of each stage being operated in hand over hand relationship so that as interpolation is carried out for one interpolator span the information relation to the next span is being set into the other bridge, and so on. The " A " bridge in the pair of bridges for the first stage (Fig. 2a) includes two auto transformers T1 and T2 arranged so that both linear and parabolic interpolation may be carried out. When linear interpolation is required the winding 84 on auto transformer T2 is shorted out so that this transformer does not operate. Input signals are fed from the stores which hold the information relating to the ends of the interpolator spans on the lines 36, and when parabolic interpolation is desired a mid point signal is fed through the normally closed contacts 42CR. The appropriate input sequence is controlled by the contacts 29CR-31CR, and the output sequence by the contacts shown on the output side of the transformer T2. The " B " bridge of the pair of first stage bridges is very similar, and the input and output lines of the two bridges are common. The outputs from the bridges are taken from the lines 86-91 and fed to the bridge inputs of the second interpolator stage. The interpolated outputs from the first pair of bridges provide the end of span inputs for the second pair of bridges. Transformers T5 and T6 (Fig. 2c) are the interpolator transformers for the " A " bridge of this second stage and inputs are received on lines 92, 93, 94 from three of the output lines of the " A " and " B " bridges of the first stage. The outputs on the three other lines are fed to the " B " bridges of the second stage. The second stage carries out quadratic interpolation between the outputs of the first stage in the usual hand over hand manner between the two bridges. The outputs from the transformer T6 are fed via the switching contacts shown to four output lines 98-101, which lines also receive the " B " bridge outputs, the signals on the output lines at any given time depending on the switching sequence of the output switches. Two output lines 102, 103 from the second stage are connected to the " A " bridge of the third stage, the other two being connected to the " B " bridge of this stage. The third stage carries out linear interpolation between the interpolated values produced by the second stage by means of tapped autotransformers such as T9. The outputs from these autotransformers are fed via a switching tree to the output 40 of the interpolator. The switching contacts within the interpolator consist of the mercury wetted contacts of reed relays and the drawings show their normal positions at the commencement of an interpolation cycle. The operation of the relays to effect the switching in the trees of the third interpolator output stage is controlled by drive arrangements operated from a shift register (Fig. 3, not shown). The shift register cycles in response to pulses received from computing circuits in the machine tool control circuitry which determine the rate at which interpolation should be carried out. Further relay switching arrangements are incorporated which effect the switching of the contacts in the second and first interpolator stages, one change in contact connections of the second stage being determined by a full cycle of the third stage, and similarly for the first stage (Figs. 4, 5, 7, 8, not shown). The relay rings for switching through the interpolated valves in the first stage are arranged so that three possible interpolator resolutions may be derived: coarse, with each first stage span divided into two sub-spans, medium, (four sub-spans) and fine (eight sub-spans). Each sub-span derived from the first stage is divided into sixteen subspans by the second interpolator stage and each sub-span from the second stage is divided into sixteen sub-spans by the third stage. The amount of resolution which the first stage is required to give is determined automatically from the span length fed to it, as determined by the voltages applied to the interpolator bridges of the first stage. If the span exceeds a certain magnitude, Zener diode switching circuits operate to actuate relay circuits to bring in a finer degree of resolution (Fig. 9, not shown). Relay circuitry is also described for switching the information from the stores to the interpolator (Fig. 10, not shown).