Patent GB-1428566-A (GB)
Title: Stroke varying mechanism
IPC: F16H21/44
Filed: 1973-08-29
Abstract: 1428566 Linkwork G C GRANT 29 Aug 1973 [13 Sept 1972 17 Nov 1972] 40572/73 Heading F2K [Also in Divisions A5 and H2] In a medical respiratory machine (Fig. 6) a crank driven oscillatable lever 10 operating a bellows type pump 35 controlling the volume of gas passed into and out of a patient's lungs per minute is pivotable about a fulcrum assembly 13 which is manually adjustable intermediate the ends of the lever to vary the stroke volume of the pump. The fulcrum assembly 13 comprises a pinion 21 meshing rack-like teeth 17 formed both on a fixed member 11 and the lever 10 (Fig. 3) the pinion 21 being freely carried on spindle 20 between slide-blocks 19, 18 located in V-form slideways 16 on the member 11 and lever 10. Manual adjustment of the fulcrum assembly 13 along the slideways 16 is effected by a hand wheel 27 operated lead screw 26 which engages and axially moves a screwed block 25 fast with the slide block 19. An indicator pointer 31 (Fig. 5) is carried by a screwed block 30 on a second lead screw 29 connected via bevel gears to the lead screw 26 to provide an indication of the position of the fulcrum assembly relative to the length of the lever 10. In the arrangement of the respiratory machine (Fig. 6) the pump 35 is connected via a 1st solenoid operated (intake) valve 36 to a gas supply line 37 and through a 2nd solenoid operated (inspiratory) valve 38 to a delivery line 39, the supply line 37 being normally connected to a source of air, oxygen or anaesthetic gas and the delivery line connected via a gas heater and humidifier 41, to an endo-tracheal tube fitting 40 for delivery of gas to the patient's lungs. A 3rd solenoid operated (expiratory) valve 42 in an expiratory line 43 of the endo-tracheal fitting 40 exhausts to atmosphere. The arrangement is such that during expansion of the bellows pump 35 (i.e. during an expiration stage) valves 36 and 42 are opened and valve 38 closed, whilst during compression of the bellows pump (i.e. during an inspiratory stage) valve 38 is opened to permit delivery of gas to the patient's lungs and the valves 36, 42 are closed, synchronous operation of the valves 36, 38 and 42 being controlled by an electrical switch 50 actuated during each cycle by a cam face of the lever operating crank plate 46 driven by a single phase A.C. line motor 49. Variable speed stepping of the motor 49 during each inspiration/ expiration cycle of the machine is controlled by ganged ratio control potentiometers 57 and 58 (Fig. 7) in series one with the other and in parallel across a motor speed control potentiometer 56 all in the gate circuit of an S.C.R. 55, the two potentiometers 57, 58 being alternatively switched into the gate circuit of the S.C.R. 55 by a switch 59 during each revolution of the cam crank plate 46, the two potentiometers 57, 58 being ganged in such manner that as the resistance of one is increased the resistance of the other is decreased by approximately an equal amount thus providing for control of speed stepping of the motor 49 during each revolution of the crank: mechanism 45 whilst the average speed of the motor 49 is maintained at a controlled constant level.