GB1240882A - Improvements relating to scale conversion apparatus - Google Patents

Abstract

1,240,882. Scale conversion device. FERRANTI Ltd. 11 Sept., 1969 [19 Sept., 1968], No. 44476/68. Heading G4A. A scale conversion device for converting N input pulses of one scale to D pulses of a closely related scale comprises means for inserting or inhibiting ID-NI evenly spread pulses. To interconvert imperial and metric scales, for example for a machine tool or a measuring probe, multiples of 001 inch (25.4 microns) are converted to multiples of 25 microns, i.e. an interconversion ratio of 127 to 125. To convert imperial to metric, electrical input pulses arrive at varying times on line 11 and are counted algebraically in a bidirectional binary counter 12 having a capacity of 125. The signs of the pulses are indicated by lines A and S. A diode decoding detector stage 13 applies a pulse over line 14 when the counter holds 31 pulses and a pulse over line 15 when it holds 93 pulses. These pulses pass through OR gate 16 and trigger a pulse delay and amplifier stage 17 to provide one pulse to OR gate 21. OR gate 21 also receives the pulses from line 11 and feeds a bidirectional counter 24. Thus for an algebraic sum of 125 input pulses at 11, 127 output pulses are received at counter 24, the extra two pulses being spaced by 125/127 - 125 #, 63 input pulses. Should the counter 12 reach 32 pulses and then count down, an appropriate negative pulse is generated. The delay in stage 17 prevents pulse loss by overlapping. When the counter 12 reaches 125 it returns to 0 and counts a fresh group. To convert metric to imperial, 127 input pulses are converted to 125 output pulses, and units 17 and 21 are replaced by an inhibit gate which suppresses two pulses per group. Instead of lines 11, A, and S, two rails may be provided, the sign of the pulse depending on the rail it arrives on (Fig. 6, not shown). A detector 13 for a 4-stage counter is described (Fig. 3, not shown) as is a unit 17 comprising two monostables. During the delay of a pulse arriving from unit 17 the sign of lines A and S may change and thus cause an erroneous pulse addition or subtraction. To prevent error a gating network (Figs. 4 and 5, not shown) generates a signal on the upward count at 32 and 93, and at 94 and 33 on the downward count). A modified counter using J-K flip-flops is described (Figs. 7 and 8, not shown), and Fig. 1 is modified using this counter in Fig. 10. On the arrival of the 31st pulse the five counter stages below stage D 5 are all one (i.e. 1111100 = 31) and stage D 5 is enabled by a pulse RD 5 . When the 32nd pulse arrives the generator 17 is triggered to give one pulse after a delay. A second single pulse is generated on the arrival of the 96th pulse. Counting down is again catered for as is modification from metric to imperial. A modification for interconverting scales of 100 and 127 is described (Fig. 17, not shown). Instead of a single pulse being added the next input pulse may be given the weight of two (Fig. 18, not shown).