IMPROVEMENTS IN OR RELATING TO STEPPING MOTORS, IN PARTICULAR MOTORS OF PNEUMATIC KIND CONTROLLED BY FLUID AMPLIFIERS

1,212,274. Fluid logic and switching circuits. SOC. GENERALE DU VIDE "SOGEV". July 25, 1968 [July 25, 1967], No.35670/68. Heading F1P. A shaft 3 is rotated in steps in one direction or the other by pneumatic actuators 8, 9 fed with gas by a fluidic circuit 27, 37, 38, 42, Fig.3, operable to cause the shaft to move through one step in response to an input signal 25 and to a signal dependent on the position of the shaft 3. Each pneumatic actuator 8 or 9 has a pawl 6 or 7 movable, when the actuator is operated, into engagement with respective ratchet wheels 1, 2 arranged to drive the shaft 3 in opposite directions. The position signal is provided by the co-operation between a perforated tape, Fig. 6 (not shown) or wheel 16 driven by the shaft 3 and two oppositely facing nozzles 18, 19 between which passes the tape or wheel. When a perforation registers with the nozzles, flow takes place from nozzle 18 to nozzle 19. To rotate the shaft through one step the input signal 25, in the form of a short pulse is sent to a pulse-shaping circuit 27 including a fluid amplifier trigger 26. The output 29 from the trigger 26 is fed to a bi-stable fluid amplifier 28 having control inputs 30, 32 including restrictions 31, 33 and a reservoir 34. This arrangement produces an amplified control pulse 35 of predetermined duration. Triggers 39 and 43 change state as a result of the pulse 35 being sent to the input 70 of the trigger 39. Operation of the trigger 43 produces an output in line 45 and thereby causes the release of a locking pawl 14 from engagement with teeth 13 of a locking wheel 12 fixed to the shaft 3. Simultaneously the output in the line 45 passes to a switch 68 selectively positioned to pass on the output to one or other of bistable amplifiers 48, 49 depending on the desired direction of rotation. Assuming the switch passes the output to the input 46 of the bi-stable amplifier 48, the state thereof is changed and fluid passes to the actuator 8 through a line 62 to rotate the shaft 3. When the flow between the nozzles 18, 19 is interrupted the fluid supply to the control inlet 69 of the trigger 39 is lost and the trigger changes state thus causing the change-over of the trigger 43. As a result the trigger 43 produces an output at 50 to cause re-engagement of the locking pawl 14 and a delayed change-over in the amplifier 48. The actuator 8 is then returned to its starting position to await re-activation when a new control pulse 25 is received. The pulse shaping circu