Patent GB-1201506-A (GB)
Title: An analog-to-digital or digital-to-analog force conversion system
IPC: F15C4/00
Filed: 1967-11-30
Abstract: 1,201,506. Fluid-pressure servomotor systems. INTERNATIONAL BUSINESS MACHINES CORP. Nov.30, 1967 [Dec.19, 1966], No.54444/67. Heading G3P. [Also in Divisions G1 and G4] An analogue-to-digital or digital-to-analogue conversion system comprises (a) a force balance beam 13 subject to opposing forces applied by bellows 17 in response to a continuously variable force and by a spring 21 whose stress is variable in discrete steps by reversible electric stepping motor 25, (b) a stress increment counter 12 to count the discrete steps from a predetermined datum and (c) automatic means (40 and 58 or 167) to adjust one of the forces to re-balance the beam following a change in the other variable force. In the analogue-to-digital system of Fig.1 any displacement of the beam 13 due to variation in the analogue input to the bellows 17 affects the pressure in a stationary nozzle 40. This pressure is detected by a pair of piston actuators 45, 46 connected to switches in a direction control circuit 58 for the stepping motor 25 which automatically adjusts the tension in spring 21 and turns a drum 30-1 in corresponding discrete steps. Binary coded slots 31 in four tracks, aligned with four nozzles 32 supplied with compressed air, allow leakage when they move selectively into register with the nozzles. The pattern of high and low pressures in the nozzle 32 can be monitored through pressure sensing taps 36 to provide the digital output. More drums 30-2, 30-3... with suitable transfer mechanism increase the capacity of the counter, which is arranged to operate in forward and reverse directions. The range of analogue values that can be digitized is selected by the choice of spring constant for spring 21 and by adjustment of a supplementary spring 20. The counter can be disconnected from a spur gear 26 while the desired spring tension on the beam is obtained. In the digital-to-analogue system of Fig.3, the digital input applied to electrically controlled valves 60 which provide either high or low pressure to the respective binary orders of a fluid operated comparator also connected to the pressure taps 36 of counter 12. When a discrepancy appears in the comparator between the two inputs, the direction control circuit 58 (and a high speed circuit 59 for discrepancies above a predetermined value) produce pulses to operate the motor 25 and vary the tension in spring 21 until the inputs are equal. Consequent movement of the beam 13 relative to the nozzle 40 varies the pressure within the nozzle 40 and controls a fluid-pressure relay 167 to vary the analogue pressure in the output duct 19 until the beam balances and the analogue output corresponds to the digital input. The valves 60 may be set simultaneously by a computer which can then be otherwise employed while the comparator controls the motor to perform the digital-toanalogue conversion. Fluid logic elements Figs. 5a, 5b (not shown) in a digital order comparing circuit Fig. 6 (not shown) are described for use in the fluid actuated comparator schematically indicated in Fig. 4 (not shown).