Patent GB-551162-A (GB)
Title: Improvements in or relating to regulating or controlling systems
IPC: G05D23/20
Filed: 1941-08-05
Abstract: 551,162. Automatic control systems. IGRANIC ELECTRIC CO., Ltd. Aug. 5, 1941, No. 9932. Convention date. Aug. 4, 1940. [Class 38 (iv)] [Also in Groups XXIV and XXXVIII] A motor-operated control system wherein the supply of a medium is varied to maintain a condition, e.g. temperature, substantially constant includes what is referred to as a negative lostmotion device whereby upon reversal of the motor, due to change in the condition, the driven element, which is directly connected to the means for varying the supply of the medium, is not only immediately engaged for driving in the reverse direction, but the rate of driving is increased for a predetermined period after which it is driven at a normal slower rate thus obviating the effect of lost-motion, reducing the period of the hunting or stabilizing cycle and giving a more accurate control. A reversible motor 15 drives, through reduction gearing, a shaft 16 at a slow speed. A pinion 18 secured to a shaft 17 has a diametrical V-groove engaged by a pin 19 passing through shaft 16. A spring 31 compressed between a bracket 33a, and a pin 35 passing through shaft 17, urges the shaft to the left to hold the V-groove in engagement with the pin 19, and another spring 32 serves to clamp a pinion 26, loose on shaft 17, between plates 27, 30 of which 27 is secured to the shaft by a pin 28 having an extension 28a. Pinion 18 meshes with a wheel 24 loose on a fixed shaft 23 and pinion 26, which is larger than pinion 18, meshes with a gear 25 also loose on shaft 23. Gear 25 directly actuates the means for varying the supply of the medium which may be blades 37a, 37b, of a potentiometer 36 or, in a modification, Fig. 6 (not shown), a valve spindle. A prong 46 rigidly attached to gear 25, Figs. 1, 3, is adapted to engage one or other of a pair of screws 48, 49 adjustably mounted in spaced lugs 29f, 29g formed integrally with a base 29 fixed to gear 24. If shaft 17 is rotating clockwise, Fig. 1, and the prong 46 abuts screw 48, the wheel 25 is constrained to move at the same rate as the wheel 24. If now the shaft 17 be reversed, gear 24 will rotate relatively slowly, but gear 25 will be free to rotate more quickly until the prong 46 catches up with and engages screw 49, whereupon gear 25 will again rotate at the speed of gear 24 and the pinion 26 will slip. The extension 28a strikes one of the lugs 29 to prevent overdrive. In Fig. 7, is shown a gas-mixing control system incorporating this negative lostmotion device. A gas of high calorific value flows through a branch conduit 54 under the control of a valve 55 and gas of a low calorific value, or air, flows through a conduit 56 the gases mixing in a conduit 57. A continuous sample of the mixture is supplied to a calorimeter 60 at atmospheric pressure through a constriction 58a, a vent in the form of a burner 61 being provided. The calorimeter is preferably of the type described in Specification 527,333, [Group XXXVIII]. Variations in temperature causes deflection of a galvanometer G and rotation of a shaft 62 an insulated arm 63 on which contacts with either 64 or 65. A conductor 66 leads from 63 to a fixed contact 67, with which normally contacts under spring load an arm 68 actuated by a cam 69 continuously rotated by. a motor 70. The system is supplied with direct current from lines L1, L2. The valve 55 is actuated by a motor 72 through a negative lostmotion device as described above and contained in a casing 72<SP>11</SP>. Changes of temperature in calorimeter 60 cause the arm 63 to move, to 64 or 65 to produce rotation of the motor 72 in the requisite direction. If the adjustment of valve 55 is not sufficient, arm 63 remains in engagement, so that during the next contact of switch arm 68, produced by cam 69. The motor 72 will again be energized to move the valve still further in the same direction, in which case there will be no lost motion and the valve will be moved slowly. The time period during which arm 68 is disengaged allows the calorimeter 60 to respond to the adjustment before another is made. If the conditions in the calorimeter call for a reverse movement of valve 55 this will be produced by appropriate movement of arm 63 and the motor 72 will then actuate the valve through the negative lost-motion device at a relatively quicker rate. For greater accuracy, the calorimeter 60 of quick-action type may be combined with a slower acting precision calorimeter 73 as described in U.S.A. Specification 1,625,277 such a combination being described in U.S.A. Specification 2,022,279. The indicating and recording portion 74 of this calorimeter includes an arm 75 connected to a fixed contact 79 with which co-operates an arm 80 actuated by cam 81 driven simultaneously with cam 69. The movable arm 84 of a resistance 83 is connected with galvanometer G and hence changes in the angular position of such arm effect corresponding changes in the calibration of calorimeter 60. The arm 84 is adjusted by a reversible motor 85 similar to motor 72 and comprising the negative lostmotion device in a casing 87. Changes of temperature in calorimeter 73 will cause the arm 75 to contact either at 76 or 77 to cause motor 85 to rotate arm 84 to calibrate accurately the control circuits of calorimeter 60. A simplified system is described in connection with Fig. 8 (not shown). A system for controlling the supply of combustible. to a heating oven is shown in Fig. 9. The gaseous fluid flows through a conduit 88 to a burner 89 in an oven 90. The current from a thermocouple 92 is utilized to operate a contact arm 93a, of a polarized relay 93 the arm being biased by a spring 93c to contact 93d when the temperature is below that desired. A circuit is then established from line L2, through contacts 95, when closed by a cam 96 actuated by a motor 97, conductor 98 and contact 93d through winding 100 of a switch with normally open contacts 100a and thence by conductors 101-103 to line L1. Contacts 100a when closed complete a circuit for motor 72 to effect opening movement of valve 55 If the oven temperature rises above that desired the arm 93a will contact 93c to energize the winding 104 of a second switch with normally open contacts 104a whereby the motor is reversed, the negative lost-motion device 72<SP>11</SP> giving an initial rapidly closing movement. Figs. 11 - 13 (not shown) are graphs showing the heating values obtained by adjustment of the valve and the indications of the calorimeter both with and without the negative lost-motion device the effect of which is seen in an earlier response of the calorimeter to the changes in calorific value and thus in a substantial reduction of the length of the hunting or stabilizing cycle and a closer and more accurate control of the total heating value.