* GB785834 (A)

Description: GB785834 (A) ? 1957-11-06

Improvements in and relating to liquid quantity measuring apparatus

Description of GB785834 (A)

COMPLETE SPECIFICATION 'Inprovements in and relatrllg to Liquid Quantity Measuring Apparatus We, .WINNEAPOLIS-}IONEYWELL REGULA- TOR COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of 2753 Fourth Avenue South, Minneapolis, Minnessota, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to apparatus for measuring the quantity of a liquid in a container, for example, fuel in aircraft fuel tanks. At the present time the most accurate fuel gauge known is the capacitive type which utilises a capacitor having plates extending from the top of the fuel tank to the bottom. Since the dielectric constant of fuel is approximately twice that of air the capacitance of the capacitor, or tank unit as it is generally called, increases to about double its previous value as the tank goes from empty to full. This measuring tank unit provides a signal which is dependent upon the height or volume of the fuel and its dielectric constant. It is frequently more important to know the weight of fuel in a tank rather than the volume, because an engine generates power in proportion to the weight or BTU's of the fuel it consumes. However, the volume of a given weight of fuel varies with change in temperature, so that a particular volume of fuel at one temperature will not weigh the same as that volume at another temperature. For the fuels used with reciprocating engines the dielectric constant of the fuel varies closely with change in volume for temperature changes. This makes it possible to multiply the volume indication by the dielectric constant and receive a signal proportional to the weight of

the fuel. For the fuels used with gas turbine engines, however, the dielectric constant does not vary proportionately with change iu volume. Therefore, in order to provide true weight indication of the fuel it is necessary to eliminate the effect of variatlons in the dielectric constant of the fuel. According to the present invention, there is provided apparatus for measuring the weight of a liquid in a container, comprising a first capacitative unit for deriving d first electrical signal proportional both to the level of the liquid in the container and to the dielectric constant of the liquid, a compensating capacitative unit automatically adjustable in accordance with variations in the density of the liquid and which operates normally totally-immersed with the liquid acting as the sole capacitor dielectric so as to derive a second electrical signal commensurate both with liquid density and with dielectric constant, and an electrical indicator circuit connecting said capacitative units whereby the first signal is modified by the second to give an output independent of dielectric constant and proportional to the weight of liquid. Preferably the compensating unit comprises a condenser having a pair of plate electrodes so proportioned, and so electrically connected in circuit with the level responsive unit, as to exactly neutralise changes in the capacity of the latter due to changes in dielectric constant of the liquid, whilst one plate of the compensating condenser is movable relatively to the other under the control of a density-responsive element to derive the component of said second signal proportional to liquid density. In the preferred form also, the densityrespons:ve element comprises a float whose density is low compared with that of the liquid, the float being secured to a lever which is in turn coupled to the movable condenser plate, and a spring tending to oppose the lift of the float. The above described arrangement operates satisfactorily for measuring the weight of fuel in tanks which remain stationary or move at relatively constant velocity at the same altitude. However, for aircraft such as fighter aircraft which accelerate and decelerate and change afti tude rapidly, changes in velocity and direction could cause errors of appreciable magnitude due to the inertia of the movable plate of the compensator capacitor. The present invention also aims at preventing this error from arising. The scope of the invention is defined in the appended cIaims, and one practical embodiment thereof will now be particularly described, by way of example only, with reference to the accompanying circuit diagram. The quantity of fuel which is to be measured is contained in a tank 10

having an outlet 11 connected to an engine or engines not shown. The fuel level gauge is connected to one arm of a modified Wheatstone capacity bridge circuit which is energised from a transformer 12 having a primary winding 13 and two secondary windings 14 and 15. A rheostat 18 has its resistor 16 connected to the secondary winding 14 and its slider 17 connected to the resistor 20 of a potentiometer 19. The other end of the potentiometer resistor 20 is connected to the other end of the transformer secondary winding 14 and also to earth. A liquid level unit 24 has an inner electrode 25 and an outer electrode 26 which are cylindrical in shape and concentric. As the level of the fuel in the tank 10 rises and falls, the capacitance of the level measuring unit 24 varies and so changes the signal derived therefrom. The outer electrode 26 of the unit 24 is connected to the slider 21 of the potentiometer 19, and the inner electrode 25 is connected to the live input side 31 of an amplifier 32. The other input terminal 33 of the amplifier is earthed. One plate of a capacitor 34 is connected to a tapping 35 on the secondarv winding 15 and its other plate is connected to the live input 31 of the amplifier 32. A tapping 40 near the other end of the secondary winding 15 is earthed. As a result the phase of the voltage across the capacitor 34 is in opposition to the phase of the voltage across the tank unit 24. The capacitor 34 has a value such that the signal from it is equal in magnitude to the signal from the tank unit 24 when the tank 10 has no fuel in it. That is, the signal frorn capacitor 34 neutralizes the no fuel component of the signal from the level unit 24. A potentiometer 38 has its resistor 41 connected across one portion of the secondary winding 15, whilst a feed back potentiometer 39 has its resistor 43 connected between the other end of the secondary winding 15 and the slider 42 of the potentiometer 38. The slider 44 of the potentiometer 39 is connected to a tapping 45 on an autotransformer 46 which is centretapped to earth at 47. One end of the autotransformer 46 is connected to the plate 52 of a compensator tank unit 50, the other plate 51 of which is connected to the live input 31 of the amplifier 32. The other enJ of the autotransformer 46 is connected to one side of a capacitor 56 the other side of which is also connected to the live input 31 of the amplifier 32. The compensator tank unit 50 and the capacitor 56 are thus connected to opposite ends of the autotransformer, and the capacitor 56 is designed so that its signal is equal in magnitude but opposite in phase to the signal from the compensator 50 when the tank 10 is empty. The amplifier 32 controls a motor 62 connected by mechanical feed back drive 63 to the slider 44 of the potentiometer 39 for rebalancing purposes, and also moves an indicator pointer 65 over a dial 66 to

indicate the quantity of fuel in the tank 10. The apparatus is calibrated as follows: With no fuel in the tank, the slider 17 s moved until the apparatus is nearly in balance, the pointer 65 indicating practic- ally no fuel in the tank. For fine zero adjustment the potentiometer slider 21 is then moved until the pointer 65 is brought to zero. At this point the slider 44 is at the earth potential end of the feed back potentiometer resistor 43. The tank is then filled with fuel. The output signal from the level unit 24 increases and causes the motor 62 to move the potentiometer slider 44 and the pointer 65. The slider 42 is then adjusted until the pointer 65 is on the full mark, the slider 44 now being at the high potential end of the potentiometer resistor 43. With the capacitor 34 balancing out the empty tank signal from the level unit 24, and the capacitor 56 balancing out the empty tank signal from the compensator unit 50, the only effective signals remaining are that from the level unit 24, due solely to fuel in the tank, and that from tank unit 50 due solely to the presence of fuel between the plates 51 and 52. Thus, the signal from the tank unit 24 is due to the height of the fuel in the tank and the dielectric constant of that fuel, and the signal from the compensator tank unit 50 is due solely to the dielectric constant of the fuel. When the apparatus is in balance, the signals from the tank unit 2 due to variation in dielectric constant value and from the tank un t 50 neutralise each other, and complete dielectric constant compensation is obtained, and the apparatus measures the volume of fuel in the tank. In order to register the weight of the fuel in the tank, it is necessary to multiply the volume signal by a density signal. This latter is obtained by making one plate of the compensator capacitor 50, for example the lower one 52, movable with respect to the other. The lower plate 52 is connected to a float 67 by a lever 70 working on a pivot 71 against a tension spring 72. The float 67 rises and falls in the fuel with change in density, and is of a material such that it is always lighter than any fuel which might be put in the tank and always works against the spring 72. Thus as the float moves the plate 52 is brought either closer to or farther from the plate 51, and the signal due to the compensator unit 50 has a component proportional to the density of the fuel as well as to the dielectric constant. Since, as explained above, the dielectric constant components in the outputs from the two tank units, 24 and 50, neutralise each other, the resultant signals are proportional to the volume of the fuel multiplied by its density, and so provide a weight indication. The circuit as thus far shown and described operates satisfactorily

for indicating the weight of the fuel in containers which either remain stationary or move with a constant velocity. However, when placed in, say, fighter aircraft, large errors could arise from the inertia of the movable plate 52 under acceleration and deceleration of the aircraft. In order to eliminate these effects, a weight 73 is also connected to the lower plate 52 by a lever 74 working on a pivot 75. This weight 73 acts against a compression spring 76 which balances the weight 73 except during acceleration and deceleration. The weight is much more dense than the fuel, and hence relatively minor changes in density of the fuel will not appreciably affect its apparent weight. In this way, any tendency by the movable plate 52 to vary the gap between it and the other plate 52 is counteracted by the weight 73 which tends to move in the same direction under acceleration of the aircraft. The present invention thus provides a simple and accurate gauge for the weight of fuel in a tank, whether static or subject to relatively high forces of acceleration. What we claim is: 1. Apparatus for measuring the weight of a liquid in a container, comprising a first capacitative unit for deriving a first electrical signal proportional both to the level of the liquid in the container and t, the dielectric constant of the liquid, a com pensating capacitative unit automatically adjustable in accordance with variations in the density of the liquid and which operates normally totally-immersed with the liquid acting as the sole capacitor dielectric so as to derive a second electrical signal com mensurate both with liquid density and with dielectric constant, and an electric-tl indicator circuit connecting said capacita tive units whereby the first signal is modi fied by the second to give an output indue pendent of dielectric constant and propor tional to the weight of liquid. 2. Apparatus according to claim l wherein the compensating unit comprises a condenser having a pair of plate electrodes so proportioned, and so electrically connected in circuit with the level responsive unit, as to exactly neutralise changes in the capacity of the latter due to changes in dielectric constant of the liquid, whilst one plate of the compensating condenser is movable relatively to the other under the

control of a density-responsive element to derive the component of said second signal proportional to liquid density. 3. Apparatus according to claim 2 wherein the density-responsive element comprises a float whose density is low compared with that of the liquid, the float being secured to a lever which is in turn coupled to the movable condenser plate, and a spring tending to oppose the lift of the float. 4. Apparatus according to claim 2 or claim 3, including means responsive .i acceleration of the container to compensate for apparent changes in density due to the response of the movable condenser plate to acceleration forces. 5. Apparatus according to claim d, wherein the acceleration-responsive means comprises a weight which acts against d resilient bias and is coupled to the mov able condenser plate in such manner that the inertia effects in the plate and weight due to acceleration of the container balance out. 6. Apparatus according to any preced ing claim wherein the electrical circuit irl- cludes a reactance bridge to which the first and second signals are fed, and means is provided for initially balancing the bridge under empty and full static conditions of the container. 7. Apparatus for measuring the quantity of liquid in a container, comprising within the container, a first capacitative sensing element connected to a source of electrical supply and sensitive to the level and the dilectric constant of the liquid so as to derive a signal commensurate with said level and dielectric constant, a second capacitative sensing element likewise connected to a source of electrical supply and totally submerged when there is liquid in the con

* GB785835 (A)

Description: GB785835 (A) ? 1957-11-06

Improvements in or relating to polyphase alternating current supply systems

Description of GB785835 (A)

PATENT SPECIFICATION 2 Inventors:-JOHN ALFRED CHIILMAN, ALFRED GEORGE MAPP. and JOHN CRIPPS. Date of filing C O omrplete Specification: Oct 5, 1955. 03 Application Date: Oct 13, 1954 No 29486154. Complete Specification Published: Nov 6,1957. Index at Acce Ltance:-Class 38 ( 4), A 1 D( 1: 2:3). International Classification:-HO 2 j. COMPLETE SPECIFICATION. Improvements in or relating to Polyphase Alternating Current Supply Systems. We, ROTOL LIMITED, a British Company, of Cheltenham Road, Gloucester, in the County of Gloucester, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to polyphase alternating current supply systems of the kind (hereinafter referred to as of the kind described) including at least two alternators driven by separate prime movers and each connectable to the bus 'bars of a load network by a separate power-actuated tie breaker switch It is to be understood that each or some of the alternators may carry an individual load when not connected to the bus bars, and that additional loads may or may not be connected directly to the bus bars. In systems of the kind described, particularly when intended for installation in aircraft, it is desirable to provide control means permitting the alternators, or any desired number of them, to be started up and connected to the bus bars of the load network in any order, or permitting one or more of the alternators to be disconnected from the network to carry an individual load. The object of the present invention is to provide a simple and effective control system for this purpose, well adapted for instalilation in an aircraft.

The present invention consists in a polyphase alternating current supply system of the kind described wherein control means for the tie-breaker switches is provided comprising, for each tie-breaker switch, a lI closing circuit including a first pair of contacts operable by means sensitive to phase displacements between the load network bus bars and the alternator associated with the tie-breaker switch so as to close said contacts at times of phase agreement within the pull-in range, a second pair of contacts closable by a time-delay mechanism which is energised upon the closing of said first pair of contacts, said second pair of contacts being closed by said time-delay mechanism after it has been energised for a predetermined time, and, for each other alternator, a further pair of contacts operable in common with the tie-breaker switch of the alternator so as to be closed when the tiebreaker switch is open and vice-versa, said further pair or pairs of contacts, when they are all closed, together short circuiting said first and second pairs of contacts, the control means also including a selective manually operable switch system permitting the closing circuits of all the tie breaker switches to be energised from a power source one at a time and in any order. According to a feature of the present invention, said selective manually operable switch system may comprise a manually operable switch which is common to all the tie-breaker switch closing circuits, and a manually operable selector switch having contacts for connecting said manually operable switch into the closing circuit of any one of the tie-breaker switches at a time. According to another feature of the present invention, each prime mover driving an alternator may be provided with a speedcontrolling device of the kind responsive to the difference between the frequencies of energisation currents supplied to two poly7855835 phase windings of an actuator forming part of the device, in which case the control means includes a manually operable selector switch adjustable into a number of settings equal to the number of alternators, each setting serving to connect one of said polyphase windings of one of said speed-controlling devices to the bus bars of the load network and the other of said polyphase windings to the alternator associated with said one of said speed-controlling devices. According to another feature of the present invention, each of said speedcontrolling devices may be of the kind in which a rotor of the actuator forming part of the device has a fixed angular position relative to the stator of the actuator corresponding to zero phase displacement of the supplies energising said two polyphase windings of the actuator, in which case said actuator may serve as the means for closing said first pair of contacts of the closing circuit of the tie-breaker switch of the alternator associated with the

speed-controlling device, the rotor of the actuator being arranged to close the contacts when it is in a range of positions, including said fixed angular position relative to the stator of the actuator, corresponding to phase agreement of the supplies energising said two polyphase windings within the pull in range of the alternator associated with the speedcontrolling device. According to another feature of the invention, in a system having the features of at least the first two of the last three preceding paragraphs, said manually operable selector switches may be operable in common, the selector switch of said selective manually operable switch system being operable to connect said manually operable switch into the closing circuit of the tiebreaker switch of the alternator of which the polyphase windings of the speed-controlling device are connected respectively to the bus bars and the alternator by the other manually operable selector switch. According to a still further feature of the present invention the system may include load adjusting means acting upon a power input-controlling device of one of the alternators to adjust the load of the said alternator into a desired relation with the load of another alternator, and switch means associated with the tie-breaker switches of the said two alternators effective to prevent operation of said load adjusting means when either of said tie-breaker switches are open. According to a still further feature of the present invention, in the case where the system has more than two alternators, the system may include load adjusting means acting upon power input-controlling devices associated one with each of the alternators to adjust the load on each of the alternators into a desired relationship with the total load on all the alternators, and switch means associated with the tie-breaker switches of all the alternators to prevent the 70 operation of each of said load adjusting means when the tie-breaker switch of its alternator is open. Said control means preferably also includes, for each tie-breaker switch, an open 75 ing circuit including a manually operable control switch individual to the tie-breaker switch In the case, where the system also includes load adjusting means for apportioning the load on one or more alternators, So the opening circuit of the tie-breaker switch pertaining to each alternator controllable by a load adjusting means is preferably separately actuable to open the tie-breaker switch by a pair of contacts operable by 85 means responsive to load on said alternator when said load exceeds a predetermined value. Two embodiments of the present invention will now be described with reference to go the drawings accompanying the Provisional Specification in which drawings:-

Figure 1 shows a polyphase alternating current supply system according to the present invention; and 95 Figure 2 shows the tie-breaker opening and closing circuits of a system as shown in Figure 1 but comprising three alternators instead of two alternators. The system shown in Figure 1 comprises 100 two three-phase alternators A, and A, driven respectively by air turbines T 1 and T 2, the speed of the turbines being controllable by variable-datum governors G, and G 2 through linkages 10, and 102 acting upon 105 throttle valves 111 and 112 in the air inlet ducts of the turbines The output lines La, Lb and Lc of the alternators are taken through main-breaker switches MB 1 and MB 2 to tie-breaker switches TB, and TB 2 110 through which they may be connected to tie bus bars Ba, Bb and Bc A load or series of loads L 3 may be supplied from the bus bars and each alternator also carries a load L, and Lo respectively which is con 115 nected to its output lines so as to be supplied whether or not the corresponding tiebreaker switches TB, or TB is closed. The tie-breaker switches are poweroperated by means of closing windings 12, 120 and 122 respectively and opening trip windings 13, and 13 respectively Since no special conditions have to be observed before opening either of the tie-breaker switches, the opening circuits which include 125 the windings 131 and 132 need comprise only a manually operable switch, 141 and 142 respectively, and a source of operating current 15. When neither of the tie-breaker switches 130 785,835 frequencies of the exciting supplies One of the stator windings of each actuator is connected by leads 21 a, 21 b, 21 c, to the output lines La, Lb and Lc of its associated alternator, and the other stator windings are 70 connected by leads 22 a, 22 b, and 22 c to the bus bars Ba, Bb and Bc, all these connections being made through switch contacts of a selector switch operated in common with the selector switch 17 as 75 indicated by the dotted line connection 23, so that when the selector switch is set, for example, to make contact at 17, for parallelling the alternator A 1 the stator windings of the actuator S, are connected as des 80 cribed, while the stator windings of the actuator 52 are disconnected When the stator windings of an actuator are thus connected, and the bus bars are already connected to the other alternator, the actuator 85 will operate upon the governor G in response to the difference in frequency between the bus bars and its associated alternator in the sense to eliminate such difference by opening or closing the throttle valve of the 90 turbine. Upon the attainment of a sufficiently close degree of synchronisation for the alternators to be able to null into step with one another, closing of the tie-breaker 95 switch can take place at any instant when the two alternators are in sufficiently close phase agreement As

already mentioned, the position of the rotor of the actuator relatively to the stator is a measure of such 100 phase agreement, and pairs of contacts 24, and 242 respectively are provided which are closed by the actuators S, and 52 in such positions of phase agreement, the operative connections being indicated by the dotted 105 lines 25 and 26 The pairs of contacts 24, and 242 are arranged in series with pairs of contacts 271 and 272 operated by time delay mechanism 28, and 282 in circuits for energising the closing windings of the tie 110 breaker switches TB, and TB 2, the time delay mechanisms operating in known manner to ensure sufficiently accurate fre. quency synchronisation before the closing of a tie-breaker switch is permitted to occur 115 The control system operates in exactly the same manner whichever alternator is to be paralleled with the bus bars and it will be sufficient therefore to trace the operational sequences for the case in which the 120 alternator A 2 is already connected to the bus bars by the tie-breaker switches TB 2 and it is desired to bring in the alternator A, To effect this the selector switch 17 is moved to the contact position 17, the 125 stator windings of the actuator S, being simultaneously connected respectively to the bus bars Ba, Bb and Bc and to the output lines La, Lb and Lc of the alternator A, At the same time, or after a brief 130 is closed the bus bars are at earth potential and may be connected directly to either, but not both, of the alternators without synchronising being necessary For this purpose each tie-breaker closing winding 12 k, 122 is provided with an operating circuit including the source 15, a manually operable switch 16 common to both circuits, a selector switch 17 which is manually oper able to make contact at 172, or 172 to limit the effect of closing the switch 16 to one circuit at a time, and pairs of contacts 181, 182 respectively which are operated in common with the tie-breaker switch of the other circuit so as to be closed when the tie-breaker contacts are open, that is to say the pair of contacts 181 is closed when the tie-breaker contacts TB 2 are open, and vice versa, this association being indicated by the dotted line connection 19 Similarly, the pair of contacts 182 is closed when the tie-breaker contacts TB, are open, as indicated by the dotted line connection 20 It will be understood therefore, that when, for 2 _ 5 example, the tie-breaker contacts TB, are open, setting of the selector switch 17 to contact 172 correspond to alternator A and closing the switch 16 results in the closing winding 122 being energised through the contacts 180 so that the tie-breaker switch TB 2 is immediately closed to connect the alternator A 2 to the bus bars At the same time the contacts 181 in the closing circuit of the winding 121 of the tie-breaker switch TB, are opened, so that this switch cannot be

operated through the contacts 181 If on the other hand, the alternator A 1 is the first to be connected to the bus bars, the closing of the tie-breaker switch TB 1 is effected in an exactly similar manner by changing the selector switch 17 over to the contact 171 and operating the switch 16, the contact 182 then opening as the tie-breaker switch TB, closes. To permit either alternator to be synchronised with the bus bars, so that both tie-breaker switches may be closed the variable datum governor G, or G respectively, controlling the turbine driving the alternator, o is controlled by a synchronising actuator S, or 52 respectively These actuators are identical and are dynamo electric machines of the kind described in British Patent Specification No 515,934 and most conveniently comprise a short-circuited rotor winding and two three phase stator windings acting differentially In these machines the position of the rotor relatively to the stator is dependent upon the phase displacement of the supplies exciting the two stator windings, zero phase displacement corresponding to either of two fixed relative positions, for a 2-pole machine, and the rate of rotation of the rotor is dependent in magnitude and direction upon the difference between the 785,835 interval, the switch button 16 is depressed and held in that position, but the tiebreaker closing winding 12, is not energised through the contacts 18, since these contacts are open The actuator 51 operates to control the speed of the turbine T, and the alternator A,1 to obtain synchronism withll the bus bar frequency set by the alternator A 2 While this is proceeding the Dair of contacts 24, closes each time the alternator A, comes into phase agreement with the bus bars within the pull in range of the alternator, and the delay mechanism 281 is set in operation Until a sufficiently close degree of synchronisation is obtained however, the time that the contacts 241 remain closed is insufficient to allow the time delay mechanism to close the contacts 271 When such closing of the contacts 271 simultaneously with the closing of the contacts 241 does occur, the closing winding 12, is energised and the tie-breaker switch TB 1 is closed, so that both alternators are now connected to the bus bars To indicate that the switch button 16 may now be released indicator lamps 291, 292 are provided in parallel with the windings 121 and 122. If it is desired to isolate one of the alternators, either to enable it to be shut down or to concentrate its output upon its own individual load, it is merely necessary to depress the corresponding switch button 14, or 142. Once the alternators have been paralleled it is necessary to provide some means for proportioning the load between them by acting upon the throttle of one or other of the air turbines In the system shown in

Figure 1 a two-phase induction motor 30 is used for this purpose in a manner more fully described in British Patent Specificatian No 732,052 and the Specification accompanying British Patent Application No 29291/5454 (Serial No 767,057) One phase winding 31 is energised by the voltage betwen the lines La and Lb of the alternator A 2 and the other phase winding 32 is energised by the difference between the currents induced in the secondary windings of current transformers CT, and CT 2 whose primaries are arranged in the output lines Lc of the two alternators In such a system the energisation of the motor winding 32 becomes zero at a particular ratio of the loads on the two alternators dependent upon the transformation ratios of the transformers CT, and CT, the load being equal if the transformation ratios are equal. The armature of the motor 30 and the synchronising actuator 52 operate the governor G 2 through a differential transmission system represented by the lever 33 Once the alternators have been paralleled the synchronising actuators become inactive and control of the governor G 2 is taken over by the 2-phase motor 30, the arrangement being such as to maintain the desired ratio between the alternator loads To prevent the alternator A becoming overloaded, a pair of contacts 38 is provided which is closed by To the motor 30 when it reaches the limit of its travel in the load-increasing direction, the said contacts completing the circuit of the opening winding 132 of the tie-breaker switch TB 2 independently of the manually 73 operable switch 14-2 When either of the alternators is disconnected from the bus bars it is necessary to put the two-phase motor out of operation, and this is done by providing two pairs of contacts 34 and 35 SG in circuit with the winding 32 of the motor and arranging for one pair to be opened when either one of the tie-breaker switches TB, or TB 2 is opened In this arrangement shown the pair of contacts 34 are operable So with the tie-breaker switch TB 1 as indicated by the chain dotted line connection 36 and the pair 35 is operated with the switch TB as indicated by the connection 37 go The control system shown in Figure 1 can be extended to cover the requirements of any number of alternators, the closing and opening circuits for a three-alternator system being shown in Figure 2 by way of 93 example From this Figure it will be seen that the number of contact positions of the selector switch 17 increases with the number of alternators, each position serving to connect the source 15 and the manually operable 100 switch 16 to the closing circuits of one of the tie-breaker switches These closing circuits are identical with those of Figure 1 except that in place of the single pair of contacts 18,, 182 it is necessary to provide 103 a pair of contacts corresponding to contacts 181, 182 for association with each other tiebreaker switch, that is to say two

pairs 40 and 41 (suffix 1, 2, or 3) in each circuit for the three-alternator system 110 In a multiple alternator system various arrangements of the load sharing system can be used, but they do not in themselves form part of the present invention and further description is considered unnecessary except 115 to Doint out that means comparable with the pairs of contacts 34 and 35 should be provided to put out of action the loadsharing control of any alternator which has been detached from the bus bars In some 120 load sharing systems each alternator is provided with a load-share corrector motor such as 30 in Figure 1 and in such a case it will be desirable to provide load limiting contacts for each alternator as shown at 125 38,, 382 and 38, in Figure 2.

* Sitemap * Accessibility * Legal notice * Terms of use * Last updated: 08.04.2015 * Worldwide Database * 5.8.23.4; 93p

* GB785836 (A)

Description: GB785836 (A) ? 1957-11-06

Improvements in or relating to welding electrode arrangements

Description of GB785836 (A)

PATENT SPECIICATION Inventor: -ROBERT HUMPHREY. Date of filing Complete Specification: Oct 18, 1955. Application Date: Oct 18, 1954 No 29930/54. Complete Specification Published: Nov 6, 1957. Inddx At Atceptance:-Class 83 ( 4), R( 2: 4 ': 8). International Classffieation -B 23 k. COMPLETE SPECIFICATION. Improvements in or relating to Welding Electrode Arangemeiits. We, THE GENERAL ELECTRIC COMPANY LIMITED, of Magnet House, Kingsway,

London, W C 2, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to welding electrode arrangements for tubes, rings and like annular members which require to be supported internally whilst a welding operation is carried out on them. It is an object of the present invention to provide a welding electrode arrangement including a clamping device which ensures that a tube, ring or like annular member to be welded makes good contact, in the region in which welding is to take place, with an electrode disposed within the member, and also prevents relative axial movement between the tube, ring or like annular member and its supporting mandrel. According to the present invention, in a welding electrode arrangement for use with tubes, rings or like annular members and comprising a mandrel carrying or forming an electrode arranged to extend within a tube, ring or like annular member, and a second electrode arranged to co-operate with the first electrode, the mandrel and the second electrode being rotatable one relatively to the other about the axis of the mandrel, clamping means are arranged within the tube, ring or like annular member for urging the surface of the tube, ring or like annular member against the operative surface of the first electrode, the arrangement being such that upon relative rotation between the mandrel and the second electrode different circumferential parts of the r Price 3 s 6 d l tube, ring or like annular member are urged into good contact with corresponding parts of the surface of the first electrode by relative displacement 'of the clamping means and the first electrode whereby a continuous welding seam may be formed. The operative surface of the first electrode may be circular in cross section, and the clamping means may be arranged to cause a part to project above this surface when in the clamping position. Said part may be a ring of similar diameter to that of the surface of the mandrel, the axis of the ring being displaced away from the axis of the mandrel when the ring is moved to the clamping position. The clamping means may comprise a pivotally mounted lever biased by spring means to move said part to the clamping position. The ring may be mounted on a spider. and ribs connecting two sections of the mandrel disposed one to each side of the ring may extend between the arms of the spider. The spider may be carried by a selfaligning ball bearing mounted at one end of the lever. A roller may be arranged to bear on that part of the tube, ring or like annular member which has been engaged by the second electrode,

after welding has taken place. One construction of electric resistance welding machine including a welding electrode arrangement according to the present invention will now be described by way of example with reference to the two Figures of the accompanying drawings in which:Figure 1 is a front elevation of part of the welding machine, the mandrel of the electrode arrangement being shown in axial section: and 785,836 45) 785,836 Figure 2 is a side elevation of part of the welding machine. The welding machine is adapted for the welding together of two overlapped metal tubes by forming two spaced-apart continuous welding seams around their circumferences, each seam being formed in a separate operation of the machine. Referring now to the drawings, the welding machine comprises a generally cylindrical hollow mandrel 1 upon which the tubes (not shown) are supported during welding, the mandrel 1 constituting one path along which welding current is carried to the welding electrodes 2 and 3 The welding electrodes 2 and 3 are cylindrical copper rings of slightly larger outside diameter than the mandrel 1, and the inside surface of the inner tube to be welded is urged into good contact with these rings beneath a roller electrode 4 by the clamping means described below The roller electrode 4 is carried by a welding head 5 mounted on the welding machine in such manner that the roller electrode 4 could be lowered into contact with the outer of the tubes to be welded and immediately above either of the electrodes 2 and 3. The main part of the mandrel 1 is rotatably supported at one end in bearings 6 secured to the framework 7 of the welding machine, and the other end of this main part is formed with a coaxial step of smaller outside diameter than the main part This step is not seen in the Figures since it is slotted radially, but two of these slots are indicated by the reference numeral 8 The step is screw threaded externally to support an internally screw threaded bush 9 carrying a hollow cylindrical extension 10 of the mandrel 1 A spacer sleeve 11 inserted in the bore of the step has a flange 12 at one end which extends between the bush 9 carrying the mandrel extension 10 and the step to ensure that an annular gap 13 around the step and between the main part and the extension 10 of the mandrel 1 is maintained when the bush 9 carrying the extension 10 is screwed on to the step The electrode 2 is secured to the main part of the mandrel 1 adjacent the gap 13 and electrode 3 is secured to the bush 9. The roller electrode 4 carried by the welding head 5 may occupy a position as directly above one or the other of the electrodes 2 and 3 and may be lowered into contact with the outer tube to be welded by operation of a control lever 14 The roller electrode 4 is urged into contact with this 630 outer tube by spring means contained within the

head 5 and which may be pre-set to apply a required contact force The tubes to be welded are arranged to be rotated past the roller electrode 4 by an electric motor (not shown) acting through a gear wheel 15 to rotate the mandrel 1 The welding machine is arranged to produce a continuous weld around the circumference of the tubes by making an overlapping series of spot welds, one seam being formed by welding 70 with the roller electrode 4 above electrode 2 whilst the mandrel 1 and hence the tubes are rotated, and another seam then being formed by repeating the operation with the roller electrode 4 occupying a position above 75 electrode 3. To ensure that the inner tube to be welded makes good contact with the electrodes 2 and 3 when in the neighbourhood of the roller electrode 4, in spite of small variations 80 in the diameter of the tube from the normal diameter, and to prevent any axial movement of the tubes on the mandrel 1, a ring 16 disposed in the annular gap 13 in the mandrel 1 is arranged to bear against the 85 inside of the inner tube on the underside of the mandrel, i e diametrically opposite to the roller electrode 4 The ring 16 may be moved to an inoperative position, in which it does not project above an imaginary 90 cylindrical surface joining the welding surfaces of the electrodes 2 and 3 so as to allow the tubes to be drawn on to the mandrel 1 before welding and to be withdrawn after welding has taken place The ring 16 is 95 carried by a spider 17 mounted by a ball bearing 18 on the end of a lever 19 which extends inside the main part of the mandrel 1 The arms of the spider 17 are disposed in the slots 8 cut in the step of the main 100 part of the mandrel 1 and the spider 17 therefore rotates on rotation of the mandrel 1 The spider 17, however, may move radially to a certain extent with respect to the step and has certain clearance in the 105 slots The lever 19 is pivoted at 20, part way along its length on a sleeve member 21 inserted in the bore of the mandrel 1 and maintained stationary during rotation of the mandrel 1 The outer end of the lever 19 110 is biased upwardly by a compression spring 22 seated on a bracket 23 secured to the stationary sleeve 21 and the ring 16 in the annular gap 13 of the mandrel 1 is thus urged to its operative position, projecting 115 just below the electrodes 2 and 3 A cam face 24 on the boss of a handle 25 bears against the outer end of the pivoted lever 19 and is arranged to force this end of the lever 19 down against the bias of the spring 22 120 in order to move the ring 16 to its inoperative position, in which it does not project beyond the electrodes 2 and 3. In operation of the welding machine the clamping ring 16 is first moved to its in 125 operative position by appropriate movement of its control handle 25 The pair of overlapped metal tubes are then drawn on to the mandrel 1 so that the overlapped portion surrounds the

electrodes 2 and 3 The 130 or like annular member for urging the surface of the tube, ring or like annular member against the operative surface of the first 55 electrode, the arrangement being such that upon relative rotation between the mandrel and the second electrode different circumferential parts of the tube, ring or like annular member are urged into good contact 60 with corresponding parts of the operative surface of the first electrode by relative displacement of the clamping means and the first electrode whereby a continuous welding seam may be formed 65 2 A welding electrode arrangement as

* Sitemap * Accessibility * Legal notice * Terms of use * Last updated: 08.04.2015 * Worldwide Database * 5.8.23.4; 93p

* GB785837 (A)

Description: GB785837 (A) ? 1957-11-06

Method of and means for casting metals

Description of GB785837 (A)

PATENT SPECIFICATION Date of Application and filing Complete Specification: November 12, 1954 No 32891/54- Application made in United States of America on November 23, 1953 Complete Specification Published: November 6, 1957 Index at acceptance:-Class 83 ( 1), F( 1 D:1 E 2:1 H:2 A), F 11 (C:E:HI:P:R:U). International Classification:-B 22 c, d. COMPLETE SPECIFICATION Method of and Means for Casting Metals I, GEORGE HARRISON, of 6901, West 30th Street, Chicago, Illinois, United States of America, a citizen of the United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and

the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a method of and apparatus for making metal castings, for use in fabricating metal products. The invention has particular utility in the casting of metals and alloys having high melting points, such as aluminum and its alloys. It is one of the objects of the present invention to provide a method of casting metals which will result in a product of uniform composition and size. It is another object of the present invention to provide a method of casting wherein the molten metal enters the mold cavity rapidly but with a minimum of turbulence. This reduces the tendency for separation of the ingredients of the metal As a result, the composition of the casting is so uniform throughout the entire mass of the casting that the casting may be used as a standard of comparison, as in spectrum spark analysis. Accordingly the invent Ion provides a method of casting metal in a mold which comprises partly immersing the mold in a bath of molten metal to introduce the metal into the mold through an entry way in the mold, applying suction to the mold to withdraw air from the mold cavity and retaining the mold partly immersed to maintain the same heated in the region of the entry way so that the metal within said region remains in a molten condition during casting and circulating a cooling medium, for example water, around the walls of the mold element forming the mold cavity to effect cooling of the remainder of the mold lPrice 3 s 6 d l to permit progressively the solidification of the cast metal inwardly from the mold walls whilst the mold so remains partly immersed so that during the time of solidification of the metal in the mold additional S(Q liquid metal flows into the mold as the metal therein shrinks upon cooling. It is a further object of the invention to provide a casting machine wherein the bottom of the die is dipped into a crucible 55 of molten metal which is then drawn into the die through the bottom of the die assembly The portion of the machine which contacts the molten metal in the crucible is removed therefrom during a por 60 tion of each casting cycle to minimize deterioration thereof by the molten metal. The invention therefore also provides a metal casting machine having a mold consisting of relatively movable mold elements 65 one of which has an open bottom mold cavity closed by the other which includes an entry-way for the flow of casting metal into the cavity from a crucible containing a bath of molten metal in which the mold 70 is adapted to be partly immersed, means for applying suction to the mold, means for circulating a cooling medium, for example water, around the walls of the mold element forming the mold cavity, means for 75

sliding one of said elements with respect to the other for severing the solidified main casting body from the solid plug remaining in said entry-way following the hardening of the casting metal, and means for 80 thereafter moving the mold elements with respect to one another to uncover the mold cavity for removing the finished casting from said mold cavity. In the preferred embodiment of the pre 85 sent invention the mold is water cooled except at its bottom face which contains the gate for the entry of liquid metal into the mold and is maintained hot during the molding operation Liquid metal flows into 90 T ' '1 c _ 785,837 the mold at a rate controlled by the evacuation of air from the mold to prevent turbulence and splashing of molten material onto the cold mold walls since that produces voids and irregularities at the casting surface The rate of exhaustion varies with the metal being cast and is adjusted to provide as high a rate of flow of metal into the mold as is possible without creating undesirable turbulence. The liquid metal entering the mold solidifies the instant it touches the water cooled side walls thereof The rising mass of liquid metal is therefore solidifying from is the outside of the mold inwardly, and from the top of the mold downwardly, while the metal at the bottom of the mold is maintained hot by contact with the hot molten material in the crucible that supplies the molten metal to the mold cavity Because of the progressive solidification of the metal toward the entry-way any shrinkage of the solidifying metal results in drawing additional molten metal into the mold cavity so that upon ultimate solidification of the metal the resulting casting is devoid of cavities. Briefly, the die of the preferred form of the invention includes an upper die element having an open bottom mold cavity, and a lower, dish-shaped die element which has a gate or entry-way in the bottom thereof The bottom of the composite die assembly is dipped into a body of molten metal to be cast Each mold cavity is evacuated at a controlled rate to draw molten metal thereinto at a controlled rate. Upon solidification of the metal in the mold cavity the die assembly is lifted from the source of molten metal, and one die element is shifted relative to the other to shear the casting from the gate slug remaining in the entry-way of the lower die element The die elements are then sepa. rated, and an ejecting apparatus ejects the gate slug from the entry-way of the lower die element Then the casting is released from the upper die element and drops onto a chute which has been moved into position and on which the casting moves to a suitable disposal location. In view of the fact that the gate slugejecting apparatus and the chute are moved between the separated die elements, safe5.5 guards are

provided to prevent such movement until the die elements are well separated from each other. The attainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawings forming a part thereof. In the drawings: Fig 1 is a side elevational view, in partial section, of the casting machine of the present invention in the ejecting position; Fig 2 is an enlarged fragmentary front view, in partial section, of the machine of Fig 1; Fig 3 is an enlarged top view of the 70 machine of Fig 1; Fig 4 is an enlarged fragmentary side view of the machine of Fig 1 in the die casting position; Fig 5 is a top view of the ejecting appa 75 ratus included in Fig 1; Fig 6 is a side view, in partial section, of the ejecting apparatus of Fig S; Fig 7 is a vertical section taken along section line 7-7 of Fig 6; 80 Fig 8 is a detailed, enlarged, vertical section of a part of the upper die assembly; Fig 8 a is an enlarged detail of a portion of Fig 8; Fig 9 is a diagrammatic view of the 85 hydraulic, vacuum, and air line circuits which control the operation of the casting machine; Fig 10 is a view corresponding to Fig. 8 and showing a modified die assembly; 90 and Fig 11 is a sectional view taken alon 3 the line 11-11 of Fig 10. In the drawings, like reference numerals indicate like parts throughout 95 A casting machine 1, embodying the present invention, includes a movable frame support 6 which carries the various instrumentalities including a composite die assembly 8 comprising relatively movable 100 upper and lower die elements 10 and 12, respectively, casting ejecting apparatus 14, and control and timing apparatus 16 which controls, in part, the sequence of operations of the casting machine 105 The machine 1 is associated with a furnace 2 which has an open-top, heat-insulated combustion compartment 18, to which a combustible gas mixture is fed by gas lines 20 A crucible 4 is suspended 110 in the chamber 18 by its peripheral flange which rests on an upper annular shoulder 22 The casting metal 26 is maintained in a liquid state by the burning gases in the compartment 18 The furnace 2 is raised 15 from the floor by the legs 28. The machine 1 is mounted on wheels 30 that ride on rails 32 The wheels 30 are secured to the bottom of a base member 34, from which extend a pair of vertical 120 upright, supporting members 36 A bracket 38, mounted on the upright members 36 adjacent to the top thereof, supports a frame base 40 which in turn supports a hydraulic device 42 which actuates the die 125 assembly 8 The bracket 38 also supports horizontal support members 44 and 46 that support the control and timing apparatus 16.

A frame assembly 50 is slidable in hori 130 785,837 3 zontal grooves 48 in the sides of the frame base 40 It includes side frames 52 joined by front and rear bridge brackets 54 and l 56, respectively The side frames 52 include X inwardly projecting rails 53 which engage 1 the walls defining the grooves 48. Bolts 59 secure dependent side plates 60 to the side frames 52 The ejecting apparatus 14 is mounted on the side plates 60 between and forwardly of the upright supporting members 36. The upper die assembly 10 includes a die block 69 of copper or other high heat conducting metal, and a water-air-vacuum is distribution block 71, bolted together and to a split-sleeve bracket 67 which is clamped to a vertically movable piston rod 64 that projects from a hydraulic cylinder 68 of the hydraulic device 42. The bottom face of the block 69 has a number of open bottom die or mold cavities 70, which in the example illustrated are cylindrical. The rate of flow of molten material into the mold is controlled by applying vacuum thereto For this purpose threaded bores 73 are formed in the block 69, one above each mold cavity 70, in each case leaving a dividing wall 71 ' between the cavity and the bore 73 Cylindrical holes 72 are formed in the wall 71 ', each hole 72 having a counter-bored upper portion 74 in which the head 77 of a plug 76 is located The head 77 is spaced from the side walls of the counterbore 74 and has circumferentially spaced nibs or projections 79 depending from the bottom thereof to provide small spaces or passageways for the flow of air between the head 77 and the wall defining the bottom of the counterbore. Each plug 76 has a shank 81 that fits within a hole 72 and terminates flush with the bottom of the wall 71 ' The celarance between the shank 81 and the wall defining the hole 72 permits the flow of air therethrough but is so small that molten metal will not flow therebetween. A plug 75 of copper or other material of high heat conductivity is threaded into each bore 73, each plug having vertical bores 78 therethrough The bores 78 slightly overlap the peripheries of the counter-bores 74 The top of each plug 75 terminates short of the upper portion of -55 the die block 69 so as to leave a cavity 80 communicating with the bores in each plug 75. The distribution block 71 is secured by screws to the top of the die block 69 Bores 82 in the block 71, each located above a plug 75, communicate at their bottom ends with the cavity 80, and at their top ends with a horizontally extending air and vacuum channel 84 By means to be described, alternate vacuum and air pressure are successively applied to the channel 84. The block 69 has a series of vertical bores 88 distributed around each

of the mold cavities 70 as closely as is possible, lor carrying cooling water A like number 70 of bores 88 ' extend upwardly from the bottom of the block 71 each overlying and communicating at its bottom with a bore 88 and at their tops intersecting one or more manifolding or cross bores 86, and 75 continuing to a series of interconnecting parallel bores 94 which are incommunicable with the bores 86 Open ended tubes 92 extend through the bores 88 ' and are threaded at their upper ends into the go block 71 and open in the bore 94 Each of the tubes 92 extends to adjacent the bottom of a bore 88 with considerable clearance between it and the bore wall Cooling water, under pressure, is circulated through 85 the water inlet duct 94 in the distribution block 71, thence through each of the tubes 92, thence through the space between the tubes 92 and the bores 88 and 88 ' to the water outlet bore 86 Water conduits or 90 lines (shown diagrammatically in Fig 9 to simplify the drawings) are connected to the ducts 86 and 94, respectively. The piston rod 64 that carries the upper die assembly is moved by a double acting 95 piston in the hydraulic cylinder 68 Hydraulic lines 96 and 96 ' communicate, respectively, with opposite ends of the cylinder 68 under control of a cam controlled valve 97 to effect the reciprocation of a 100 double acting piston therein to which is connected the piston 64 that carries the upper die assembly. Apparatus is provided for accurately positioning the lower die assembly pre 105 paratory to the filling of the mold cavities, and for moving it laterally following the solidification of the castings to separate the castings in the upper die assembly from the lower die assembly This apparatus in 110 cludes a vertically extending cam control rod 112 secured to the rear of the splitsleeve clamping bracket 67 by a nut 110, and has a cross bar 114 secured to its upper end as by a nut 113 Cam rollers 116 115 are connected to the ends of the cross bar by bolts 118 threaded into the cross bar. As the upper die assembly 10 is raised and lowered they actuate a pair of slotted cam plates 120 which are fixed to the side frame 120 members 52 of the horizontally movable frame assembly 50 Each cam plate 120 has a vertical slot 122 having a forwardly offset lower vertical slot portion 124 When the hydraulic device 42 moves the upper die I 25 assembly 10 and cam rollers 116 downward, the cam rollers 116 enter the cam slots 122 and move the cam plates 120 rearwardly In so doing, the cam plates guide the lower die assembly 12, which is 130 785,837 carried by the movable frame assembly 50, into proper position relative to the upper die assembly When the upper die assembly is in its lowermost or casting position (Fig 4), the cam rollers 116 rest on the bottom of the cam slots 122 Following the formation of solid castings, the hydraulic device 42 moves the cam rollers 116 upward.

The lower die assembly 12 includes a flat botom pan 130, made of a suitable high melting point alloy, and having upwardly extending side walls 131 and a flat bottom 132 A plurality of gates or entryways 134 having outwardly flared bottom ends extend through the bottom 132 of the pan 130, and are spaced the same distance apart as the centers of the die cavities 70 in the upper die assembly 10 These entryways 134 constitute sprues for the die molds The pan 130 includes a peripheral flange 136 which rests on an annular shoulder 138 in a pan support ring 140. Pan guide bars 142 are provided on opposite sides of the hydraulic cylinder 68 and the bottoms thereof extend through apertures in diametrically opposite sides of the pan support ring 140 Nuts 144 threaded on the lower ends of the pan guide bars support the ring 140 from the pan guide bars 142. Split collars 162 are secured to the bottom portions of the pan guide bars 142 it pair of similar split collars 164 are secured to the upper portions of the pan guide bars 142, and act as stops for supporting compression springs 168 which surround the respective pan guide bars 142 The lower ends of the springs 168 rest against the upper surface of respective pillow blocks which are secured to the side frame members 52 of the horizontally movable frame assembly 50 A pair of lower pillow blocks 172 are secured to the side frame A 4 members 52 and act as stops for the upwardly spring urged pan guide bars 142 by their abutment with the upper faces of the split collars 162 The compression springs 168 normally bias the pan guide So bars into a position where the bottom of the pan 130 is supported above the top of the crucible 4, as shown most clearly in Figs 1 and 2. Before the machine is initially put into operation, the pan 130 is heated red hot. as by dipping the bottom thereof into the molten metal for a time sufficient to accomplish such heating The machine is then ready for the initiation of the automatic casting operations These operations include the submerging of the bottom portion of the die assembly into the body of molten material in the crucible 4 where the mold cavities are filled with molten material rapidly and without turbulence, and where the metal is caused to progressively solidify toward the gates or sprues in the bottom of the assembly; and the subsequent raising of the die assembly out of the crucible 4 and the removal of the finished castings 70 from the die assembly. It is desirable that the rate of flow of molten material into each mold cavity be determined mainly by the rate of exhaus tion of each mold cavity rather than by the 75 hydrostatic pressure head of the body of molten material above the bottom of the unfilled portion of each mold cavity If the rate of filling were to be determined to a

large extent by the hydrostatic pressure 8 e head, then the rate of filling of the cavities would decrease as the mold cavities gradually fill so that much valuable time would be lost Therefore, to minimize the time required to fill the mold cavities and 85 to minimize the effect of the depth of submergence of the die assembly in the crucible, the depth of submergence of the die assembly in the crucible is reduced to a value where the rate of exhaustion of the 9 C mold cavities primarily determines the rate of flow of the molten material therein. Where the mold cavities have a constant horizontal cross sectional area, as with the cylindrical cavities illustrated in the draw 95 ings, the rate of exhaustion of the mold cavities necessary to fill the cavities at a constant and rapid rate just short of creating turbulence is a fixed and constant amount for a given casting material A 100 ' variation in the viscosity and surface tension of the casting material varies the flow characteristics thereof and changes the optimum rate of cavity exhaustion to provide a rate of flow into the mold cavities 10 ' just below that creating undesirable turbulence In any particular case, this rate of cavity exhaustion may be determined experimentally by running several trial runs 10 The casting operation performed by the machine is as follows: The actuation of a cam controlled valve initiates the operation of the hydraulic device 42 to effect the downward movement 115 of t"e upper die element 10 The die block 69 is moved downward first into engagement with the bottom of the pan 130 and. upon continued downward movement, moves the pan 130 downward, against the 120 force of the springs 168, into the molten material 26 in the crucible 4 The upper portion of the pan 130 remains above the motlen material The engagement of the cam rollers 116 with the bottom of the slots 1 " 2 122 of the cam plate 120 accurately positions each of the die cavities 70 of the upper die assembly over one of the entryways 134 of the pan 130 The molten material then enters each mold cavity 13 C 785,837 785,837 through its entry-way 134 at a rate inhi U 3 biting turbulence as controlled by the rate si of evacuation thereof by a source of low pressure connected to the top of each mold e cavity through the clearance space between a the plug 76 and the hole 72 The molten c material rises in each mold cavity as air is exhausted therefrom When the molten t material reaches the top of each mold r cavity, entry of molten material into the cavity comes to a halt since the molten s material cannot flow through the small f space between the plug 76 and the wall of the hole 72 in the top cavity wall 71 ' 1 The solidification of the metal is then effected while the mold assembly remains partly submerged below the surface of the molten material 26 The molten metal filling each mold cavity solidifies

progressively toward the entry-ways 134, since the side and top mold walls are water cooled, and the pan bottom is maintained in contact with the hot body of molten material 26. Any shrinkage of metal:n the cooling of the liquid metal will be taken up by the liquid metal beneath the solidified metal, which liquid metal is in turn replaced by metal drawn into the entry-ways 134 from the main body of molten materal 26 The non-turbulent flow of liquid metal into the cold mold cavity and the progressive and rapid solidification of the metal in the mold cavity produces cast products of homogeneous composition. After the metal solidifies through the entry-ways 134, the hydraulic device 42 raises the composite die assembly out of the crucible 4 The pan 130 rises with the upper die under the action of the springs 168 Before the collars 162 engage the pillow blocks 172, that is, before the upper die separates from the pan, the cam plates are moved forwardly by the cam rollers 116 so that the pan is moved laterally of the die block 69 to shear the castings ' in the die block cleanly from the solid slugs 179 within the pan entry-ways 134. The slugs and cast Ings are sheared along a horizontal plane which is coextensive with the flat bottom of the pan 130 This insures that the castings have a uniform shape and quantity of material. Just prior to the vertical separation of the die block 69 from the pan 130, a very low pressure is applied to the top of the mold cavities to hold the castings in the mold cavity by suction. When the hydraulic device 42 has moved the die block 69 to its uppermost position, a control arm 98 projecting from the rear of the hydraulic cylinder 68 actuates a control rod 102 of a valve 100 which is secured to the movable cam control rod 112 This initiates movement of the ejecting apparatus 14 into a position between the die lock 69 and the pan 130 for ejecting the ugs 179 in the pan entry-ways 134. The avoidance of a collision between the jecting apparatus 14 and the upper die assembly 10 is assured, since the movement 7 G, of the ejecting apparatus toward the die Lssembly is controlled by the position of he upper die assembly The speed of movenent of the hydraulic apparatus 42 which noves the upper die assembly 10 varies 75 somewhat with the viscosity of the hydraulic luid so that collision between the upper die assembly and the ejecting apparatus is possible if the movement of the ejecting apparatus 14 is not controlled by the actual 80 position of the upper die assembly. The ejecting apparatus 14 includes a horizontal supporting base member 180 which extends between, and is bolted to, depending side plate members 60 of the 85 horizontally movable frame assembly 50. The ejecting apparatus thus moves as a unit with the pan 130 under the control of the cam plates 120 to insure a proper and constant

orientation between the pan and the 90 g ejecting apparatus The base member 180 has an inverted T-shaped slot 181 which slidably receives a rectangular shaped gib 183 in the bottom thereof Extending into the slot 181 and secured to the top of the gib 95 183 is a chute support member 206 which has an inclined upper rear surface 207 on which rests a forwardly and upwardly inclined chute 209 secured for movement with the chute support member The chute 209 100 l has upwardly extending side walls 211 defining the sides of a channel for guiding completed castings dropped thereon fromt the upper die assembly 10 to a storage bin. The front end of the chute support mem 105 ber 206 is connected to a piston rod 192 of an air pressure actuated device 188 by a plate 196 from which extends a stud 198. The stud is received in an opening in the piston rod 192 and is held in place within 11 o the opening by any suitable means, such as by the cotter pin 199 The plate 196 is bolted to the chute support member. A cylinder mounting bracket 182 is secured to the ejector base member 180 and 115 it has at its rear an upwardly extending arm 184 which is apertured to receive a pivot pin 185 The device 188 has a cylinder 190 which is supported on the pivot pin 185 by spaced apertured ears or lugs 193 which 120 straddle the arm 184 and receive the pin Longitudinal movement of the pivot pin 185 relative to the mounting bracket 182 is prevented by cotter pins 194 extending through apertures in the ends of the 125 pivot pin 185 The cylinder 190 rests on a shoulder 191 on the mounting bracket 182 which insures a horizontal orientation of the piston rod 192 projecting forwardly from the front end of the cylinder 190 130 785,837 A piston within the cylinder 190 actuates the piston rod 192 and the gib 183, chute support member 206, and chute 209. The air inlet lines 106 and 108 (Fig 9) associated with the valve 100 communicate with opposite ends of the cylinder to actuate the piston therein in opposite directions. A carrier plate 200, secured to the end of the chute support member 206, has laterally extending arms 202 projecting from opposite sides of the forward end thereof The front, outer ends of the cross arms 202 are cut away at 204 to provide a curved abutment against which the pan guide bars 142 rest when the carrier plate 200 is in its forwardmost position, as shown in Figs 5 and 6. This accurately positions the carrier plate with respect to the pan 130 An air actuated slug-ejecting device 240, to be described, is supported from the front end of the carrier plate 200. When the upper die assembly 10 is in its uppermost position and the control arm 98 has depressed the control rod 102 -of the valve 100, air pressure is applied to the right-hand end of the cylinder 188

(Figs 1 and 5) via air input line 104 and air output line 108, and the piston 192 is moved to the left, thereby carrying the ejecting device 240 and the chute 209 with it into position between the upper and lower die asemblies 10 and 12 When the die assembly 10 is in a position other than its uppermost position, the valve rod 102 is out of engagement with the control arm 98, and the air input line 104 is connected to the line 106 leading to the left-hand side of the cylinder 188 which maintains the ejecting apparatus to the right out of the way of the upper die assembly. The air actuated ejecting device 240 includes an air-operated cylinder 242, a movable piston 244 therein, and a depending piston rod 246 which carries on the bottom thereof upper and lower ejector plates 248 and 250, bolted together Depending pin members 252 are secured to the lower ejector plate 250 and are spaced to overlie the respective aperatures 134 at the bottom of the pan 130. Air inlet lines 256 and 258 (Fig 9) are connected, respectively, with the upper and lower ends of the cylinder 242 Air under pressure is alternately applied to the air inlet lines 256 and 258 under the control of a cam operated air valve 260, to be hereinafter described At the appropriate moment following the positioning of the ejecting apparatus above the pan 130, air is applied through the air line 256 to the upper part of the cylinder 242 to force the piston 244 downward, thereby causing the ejector pins 252 to eject the solid slugs 179 from the apertures 134 They fall into the crucible 4. To assure accurate orientation of the ejector pins 252 with respect to the pan apertures 134, a guide rod 262 is secured to the ejector carrier plate 200 The rod 262 extends through a guide aperture 264 in the upper ejector plate 248 and secures the ejector plates 248 and 250 against rotation 70 about the axis of the piston rod 246. Following the ejection of the slugs 179, the cam controlled air valve 260 shuts off the supply of air pressure to the air line 256 and applies pressure to the line 258, 75 thereby raising the piston rod 246 and attached ejector plates and pins out of the pan 130 The ejecting apparatus is thenretracted rearwardly of the machine and out of the path of movement of the upper die 80 assembly preparatory to the initiation of the next casting operation. Valve apparatus is provided for controlling the pressure in the die cavities This apparatus includes valve members 214 and 85 216 which are secured to the ejector apparatus mounting bracket 182 These valve members include movable control rods 218 and 220, respectively, which, when the chute 209 is in its forwardmost position where it 90 underlies the upper die assembly 10, abut a movable control arm 230 depending from, and movable with, the chute 209 This actuates the valves 214 and 216 to interrupt the vacuum applied to the mold

cavities 70 95 in the die block 69 and apply a relatively high air pressure thereto to eject the solid castings Since the valves 214 and 216 are controlled directly by the control arm 230 moving with the chute 209, ejection of the 100 castings from the upper die assembly 10 occurs only when the chute 209 is in position to receive the castings. Connected to the air valve 216 (Fig 9) is an air input line 236 and an air output 105 line 238 connecting the die cavities 70 of the upper die assembly 10 via line 239 The air input and output lines 236 and 238 are interconnected by the air valve member 216 to apply high pressure to the mold cavities 110 when the control rod 220 thereof is in contact with the control arm 230. A vacuum input line 232 and a vacuum output line 234 connect with the vacuum valve 214 When the control rod 218 is 115 removed from the control arm 230 by the rearward movement of the chute 209, the vacuum valve 214 connects the vacuum input line 232 with the vacuum output line 234 This applies low air pressure to the 120 mold cavities of the upper die assembly 10 via the line 239 to exhaust the air in the mold cavities 70 to draw molten material therein, in a manner previously explained. The input line 232 is connected with a 125 vacuum header line 241 leading to a vacuum pump 270 through the valve 215, and through an adjustable bleeder valve 257 connected across the valve 215. The adjustable bleeder valve 257 may be 130 785,837 a conventional needle valve which may be adjusted in small incremental amounts between a position where the valve is almost completely closed and a position where the valve is completely open In this manner the valve of low pressure at the output side of the needle valve 257 may be adjusted between vacuum or the low pressure output of vacuum line 241 and, say, atmospheric pressure The adjustable bleeder valve 257 determines the low pressure condition of the mold cavities 70 during the filling operation and so controls the rate of filling of these cavities in a manner previously explained The valve 215 remains closed during the filling of the mold cavities so that the bleeder valve 257 will then control the pressure in the mold cavities The needle valve is adjusted by a trial and error method, to a position where the rate of exhaustion of the air from the mold cavities causes a rate of flow of molten material therein which is just short of the point where the turbulence of the inflowing molten material forms air holes and irregular surfaces in the finished castings. A gauge 259 connected at the output of the bleeder valve 257 indicates the pressure at this point The gauge will indicate when _ 30 the mold cavities are full since the pressure will then suddenly drop due to the termination of the flow of air from the mold. The bleeder valve 257 is by-passed when the vacuum valve 215 is opened

The opening of the vacuum valve 215 applies the lowest air pressure available in the header line 241 to the mold cavities to provide maximum suction so as to maintain the solid castings in the mold cavities following -the A 40 separation of the upper and lower die assemblies. The timing and control apparatus 16 includes an electric motor 261 which is supported on the horizontal support member 44 associated with the bracket 38 A vacuum pump 270 is supported on the member 46. The motor 261 drives the vacuum pump 270 by a belt 266 which engages the grooved wheels 262 and 268, respectively, connected to the shafts of the motor 261 and the vacuum pump 270 The motor shaft also drives a speed reducer 278 through a belt 264 which engages the grooved wheel 262 and the grooved wheel 274 on a shaft 276 -55 of the speed reducer 278 Through suitable gearing within the speed reducer, cams 280, 282 and 284 on a common shaft are slowly rotated and actuate, respectively, the hydraulic control valve 97, the air pressure 460 valve 260, and the vacuum valve 215 The valves include respective control rods 290, 292 and 294 which ride on the peripheries of the respective cams 280, 282 and 284. These cams are appropriately shaped so that during a single rotation of said cams, the control rods 90, 292 and 294 are actuated to control the sequence of operations of the various movable elements of the casting machine. The cam 280 actuates the valve 97 which 70 controls the movement of the upper die assembly This valve (see Fig 9) receives hydraulic fluid, such as oil, through a hydraulic input line 298 The hydraulic lines 96 and 96 ' are connected between the out 75 put side of the valve 97 and the upper and lower portions, respectively, of the hydraulic cylinder 68 To initiate the downward movement of the upper die assembly, the cam 280 depresses the control rod 290 which 80 connects the hydraulic input line 298 to the hydraulic line 96 through the valve 97 to carry hydraulic fluid to the upper end of the hydraulic cylinder 68, thereby moving the piston therein downwardly The oil pre 85 viously filling the bottom of the cylinder 68 is returned via the line 96 ' and return line 302. When the piston in the cylinder 68 has reached its lowermost position, the casting 90 operation previously described commences. At a given time, after the complete solidification of the molten material within each die cavity 70, the cam 280 allows the control rod 290 of the valve 97 to move outwardly, 95 thereby connecting the hydraulic input line 298 to the hydraulic output line 96 ' The hydraulic fluid from the line 298 flows to the bottom of the hydraulic cylinder 68 thereby moving the piston upward therein to raise l JOJ the die block The hydraulic fluid in the upper portion of the cylinder

68 flows via the hydraulic line 96 and valve 97 to the return line 302. A hydraulic valve 291, similar to the valve 105 97, and having a hand-operated control rod 293, is connected in parallel with the hydraulic valve 97 so that the hydraulic movement of the die assemblies 10 and 12 can be controlled manually, as preparatory 11 to the initiation of the automatic operations. The cam 282 actuates the valve 260 which controls the operation of the slug-ejecting mechanism 240 The air header line 107 connects with the input side of the air 115 pressure valve 260 When the ejecting device 240 has been moved to a position over the pan 130, following the termination of a casting operation, the cam 282 actuates the control rod 292 of the valve 260 to connect 12 ( the air line 107 to the air line 256 leading to the upper end of the cylinder 242, to cause downward movement of the ejecting pins 252 Reverse movement of the control rod 292 following the ejection of the slugs 125 from the entry-ways 134 of the pan 130 causes the valve 260 to connect the air header 107 to the air line 258, which leads to the lower end of the cylinder 242, to raise the ejector pins 252 from within the 130 pan 130. The cam 284 actuates the valve 215 to control the timing of the application of suction to the die cavities 70 to maintain the finished castings to the upper die assembly when the upper die assembly separates from the pan 130 When the molten material in the mold cavities 70 has solidified, and just prior to the separation of the JO lower and upper die assemblies, the cam 284 actuates the control rod 294 of the valve 215 to open the valve and connect the vacuum header line 241 directly with the line 232 At that time, the control arm 230 has X 5 been removed from the control rod 218 of the vacuum valve 214, so that the valve 214 connects the line 232 to the line 239 leading to the distribution block 71 where vacuum is applied to the upper portion of the mold cavities to secure the solid castings to the upper die assembly by suction. A review of the sequence of operations of the various components of the casting machine is as follows: Under the control of the cam-operated hydraulic valve 97, the upper die assembly is moved downward to initiate a new casting operation With the initiation of the downward movement of the die block 69, the valve 100 is actuated by the removal of the control rod 102 from contact with the control arm 98 which causes air under pressure to flow to the left hand side of the cylinder 190 associated with the ejecting apparatus 14, to move the ejecting apparatus rearwardly or away from the pan The die block 69 then depresses the pan 130 into the molten material 26 in the crucible 4 in its downward movement, whereupon the mold cavities 70

begin to fill rapidly but without turbulence of the molten material, the adjustable needle valve 257 having been previously adjusted to provide the necessary vacuum for a maximum nonturbulent rate of flow of the molten material 4 into the mold cavities After the cavities have been filled and the casting maternal has solidified, the vacuum control valve 215 is opened which applies vacuum to the mold cavities independently of the valve 257 The hydraulic valve 97 is actuated by the cam 280 to raise the die block The pan 130 is shifted to shear the castings from the slugs in the pan entry-ways 134 The control rod 102 of the valve 100 is depressed by the control arm 98, which actuates the device 188 to move the ejecting apparatus 14 into operative position between the die block 69 and the pan 130 Valves 216 and 214 are then actuated and vacuum is removed from the mold cavities 70 and air pressure is applied to eject the castings from the mold cavities, which fall onto the chute 209 on which they slide, by gravity, from the machine A new casting cycle is initiated by the cam 280 as it actuates the valve 97 to begin the downward movement of the die block 69, following ejection of the slugs from the pan entry-ways and the removal of the castings from the die cavities 70. The vacuum method of retaining the solid 7 G castings to the upper die assembly 10 following the separation of the upper and lower die assemblies may be unsatisfactory where the solid castings are of appreciable weight or where the top surface of the castings are 75 curved In such case, the ejection of each casting from the upper die assembly may be effected by one or more air pressure operated ejector pins as illustrated in Figs. and 11 This modified upper die assembly 80 ' includes a lower cylindrical die block 300 having open bottom mold cavities 301, intermediate cylindrical distribution blocks 302 and 304 which aid in directing cooling water, air pressure, and vacuum to the die 85 block 300, and upper cylindrical members 306 and 308 which together form an airoperated piston device having casting ejector pins 310 This assembly is mounted on the piston rod 64 by the split sleeve 67 90 The mold cavities 301 have vertically extending side walls which have a very slight inward flare 313 at their bottoms The width of each flare 313 is such that shrinkage of the metal in the mold cavities upon 95 solidification thereof provides a press fit between the outer vertical walls of the castings and the openings defined by the flares 313 so that the castings are held in the mold due to the friction at that press fit The 100 castings may then be readily ejected from the mold cavities by the push of the ejector pins 310 against the tops of the castings. The upper portion of the die block 309 has vertically extending bores 314 in each 105 of which is located a vertically movable ever'or pin

310 that depends from a piston 316 The clearance between the ejector pins 310 and the walls defining the vertical bores 314 is so smnall as to prevent the rise of 110 molten material therein while allowing the passage of air therethrough The bores 314 also serve as passageways for the application of vacuum to the molod cavities 301 tc A control the rate of flow of molten material 115 to effect the circulation of cold water through th 3 die block 300, an undulating horizontally extending slot 318 is cut in the upper face of the die block 300 to provide 1 I a passageway for cold water above the mold cavities 301 A gasket 320 overlies the top surface of the die block 300 and covers the open tops of the slots 318 to provide a closed passageway for the circulation of the cooling 125 medium The gasket has openings through which the ejector pins 310 pass. The lower distribution block 302 includes a water inlet passageway 322 which communicates with one end of the slot 318 130 a 1,8 3 7 ar 785,837 through an aperture in the gasket 320 The block 302 also includes a water outlet passageway 324 which communicates with the other end of the slot 318 through an aperture in the gasket 320 The die block 300, as is the die block 69 previously described, is made of material of high heat conductivity, such as copper, so that the walls of the mold cavities 301 are cooled very quickly to effect a rapid and progressive solidification of the molten metal within the mold cavities toward the entry-ways in the pan 130 associated with the lower die assembly. The lower distribution block 302 includes vertical bores 328 in register with and of the same size as the bores 314, to receive the ejector pins 310 It also includes an air receiving passageway 330 which communicates at the upper face of the lower distribution block 302 with a cylindrical cavity 332 at the bottom of the upper distribution block 304 in which each of the bores 328 open. The upper distribution block 304 also includes vertical bores 336 which slidably receive the ejector pins 310 An annular gasket 338 is inserted between the peripheral abutting portions of the upper and lower distribution block to effect an air-tight seal therebetween. The air and vacuum line 239 is connected to a nipple at the inlet end of the passageway 330 in the side of the lower distribution block 302 The vacuum is thereby applied to the mold cavities 301 to exhaust the air from the mold cavities to effect the controlled filling thereof in a manner similar to that previously explained in connection with the embodiment of Figs 1 through 9 Air pressure is applied to the mold cavities via the same path during the ejecting of the castings to remove any dust particles gathering in the spaces between the ejector pins 310 and the bores 328 and 314. The ejector pins 310 have enlarged heads 340 which are threaded in

tapped counterbores 342 in the upper face of the piston 316 which reciprocates in a cylindrical bore 318 ' In the uppermost position of the piston 316, the bottoms of the ejector pins are flush with the tops of their associated mold cavities. A sealing gasket 344 is fitted between the bottom of the hollow cylindrical member 308 and a cylindrical plate or block 306 on the block 304 The plate 306 and the gasket 344 have bores in registry which receive the shanks of the ejector pins 310 A cylindrical recess 346 which is vented to the atmosphere is formed in the bottom face of the plate 306 and receives a plurality of annular gaskets 348 whch surround the ejector pins. The gaskets are under compression and effect an air-tight seal with the adjacent walls of the ejector pins, plate 306 and the upper distribution block 304. The piston 316 is reciprocated by air pressure applied alternately above and below the piston A passageway 350 in the side 70 walls of the hollow cylinder 308 communicates with the upper portion of the bore 318 ' A passageway 352 in the plate 306 communicates with the bottom of the bore 318 ' The passageways 350 and 352 are con 75 nected to a cam controlled valve driven by the motor 261 to apply air pressure at the appropriate times to the passageways 350 and 352 alternately, while opening to the atmosphere the particular passageway 350 or 80 352 that is not being connected to the source of air under pressure. The operation of the casting ejecting, portion of the upper die assembly is as follows: The upper die assembly 10 ', with the 85 piston 316 raised, is moved into engagement with the pan 130 and into the crucible 4 where the mold cavities 301 are filled by evacuating the air therefrom through the bores 314 all by operating the piston rod 64 90 in the manner previously explained Following the filling of the mold cavities and the solidification of the molten material therein. the upper die assembly 10 ' is raised from the pan 130 The solid castings are main 95 tained within the mold cavities by a tight fit between them and the opening at the open bottoms of the mold cavities The castings are then ejected by causing downward movement of the ejector pins Follow 100 ing the ejection of the castings, the piston 316 is raised and the above described process is repeated.

* Sitemap * Accessibility * Legal notice * Terms of use * Last updated: 08.04.2015

* Worldwide Database * 5.8.23.4; 93p

* GB785838 (A)

Description: GB785838 (A) ? 1957-11-06

Improvements in or relating to automatic control systems for impedancematching networks

Description of GB785838 (A)

A high quality text as facsimile in your desired language may be available amongst the following family members:

DE1001731 (B) ES224484 (A1) US2834887 (A) DE1001731 (B) ES224484 (A1) US2834887 (A) less Translate this text into Tooltip

[83][(1)__Select language] Translate this text into

The EPO does not accept any responsibility for the accuracy of data and information originating from other authorities than the EPO; in particular, the EPO does not guarantee that they are complete, up-to-date or fit for specific purposes.

PATENT SPECIFICATION Inventor: THOMAS THEODORE BROWN Date of filing Complete Specification Aug 5, 1955. Application Date Nov 18, 1954. Complete Specification Published Nov 6, 1957. 7859838 No 33396154. Index at Acceptance: -Class 38 ( 4), R( 2 A 1: 23: 29). International Classification: -GO 5 f. COMPLETE SPECIFICATION Improvements in or relating to Automatic Control Systems for Impedance Matching Networks We, MARCONI'S WIRELESS TELEGRAPH COMPANY LIMITED; a company organised under the laws of Great Britain of Marconi House, Strand, London, W C 2, do hereby declare the invention, for which we

pray that a patent may be granted to us, and the method by which it is to be performed, to me particularly described in and by the following statement: - This invention relates to automatic control systems for impedance matching networks such as are commonly employed for coupling a so-called self-tuning radio transmitter to its associated aerial. The invention is illustrated in and explained in connection with the drawings accompanying the provisional specification in which Figure 1 is a block diagram of a typical known automatic control system; Figure 2 is a graphical figure illustrating a defect of the known, system of Figure 1; Figure 3 is a block diagram, much simplified, of one embodiment of the invention; and Figure 4 shows the arrangement of Figure 3 in more detail. Referring to Figure 1 a transmitter (not shown) connected at terminals 1, is coupled to its load, usually an aerial but represented by a resistance Ra through a variable impedance matching network shown as of the ir type and comprising a series variable inductance Ls which is adjusted to maintain resonance (i e is a tuning control) and a shunt variable inductance L, which is adjusted to maintain impedance matching with a selected value of load resistance, e g 50 ohms to quote a practical figure Each of these inductances is automatically adjusted by its own adjusting motor MA or MB, the tuning control motor MA being controlled by a suitable phase discriminator network A and the impedance matching adjustment control motor BM being controlled by a suitable impedance comparator B The phase comparator A compares its input and output phase and so long as the relative phase condition is not that appropriate to resonance, provides a direct current output dependent on the departure from the resonance condition to control the motor MA to run in the direction necessary to restore resonance Similarly the impedance comparator B compares its input and output impedances and provides a control DC to run the motor BM to obtain and maintain the matched impedance condition. This known system has a defect which will be explained in connection with Figure 2 and which arises from the fact that all impedance matching networks have more than one frequency of resonance, i e for any given frequency from the transmitter there will be two values of adjustment of inductance L that will provide resonance At only one of these, however, will correct impedance matching bc: obtained, the other giving an unmaintainablc overloaded condition The location of the two resonance points is shown in Figure 2 which is a locus diagram of input admittance of the impedance network for variations of the value of the inductance L, over a complete range from L,, to L,4 In Figure 2 the ratio of load resistance Ra to input reactance XL (reactive impedance component at terminals 1) is plotted

against the ratio of load resistance R, to input resistance RL (resistive impedance component at terminals 1) for la few selected values of the inductance L, The locus of these points lies on a circle and the required values of L, which give resonance are the points L,, and Ls, where the circle cuts the Ra/RL axis These points also give the two corresponding values of input reactance The normally useful point is the left hand one L,,, the right hand point L,, corresponding to the overloaded condition when the Q value of the circuit is less than unity For any particular value of L, the impedance as seen by the impedance comparator B is given by the vector Ra/ZL (ZL is the impedance at terminals 1) and the phase angle as seen by the phase discriminator A is given the angle 0 In Figure 2 the quantity X Ip is the reactive impedance component of the inductance L,. Suppose now the motor MA runs to vary the impedance L, from L,, through L,, and Ls 3 to L 4 From L,, to L,2 the phase angle as seen by the phase discriminator A is lagging; at L,2 (the desired condition) the angle is zero; from L,2 to L,, the phase angle is leading; at L,, it is again zero (the unwanted resonance position); and from L,, to L,4 it lags once more Accordingly if the control of the motor MA is such as to reduce the value of inductance L, for a lagging phase angle (as seen by the discriminator) and to increase it for a leading angle, once the system reaches an operating point between L,, and L,4 the motor MA will be controlled to run in the wrong direction, i e to increase the inductance L, instead of reducing it The control system is then completely disabled It is not possible practically to avoid this trouble by providing a mechanical limit to the range of adjustment of inductance L, because the points L,2 and L,, may be anywhere on the length of the inductance, depending on the frequency and on the load Also, in practice, the points L,, and L,, tend to be close together physicallyoften only about one or two turns apart on a typical 20 turn inductance coil L,-and accordingly inertia effects in the motor MA may easily cause overshooting into the L,,-Ls 4 region The object of the present invention is to avoid the foregoing defect of liability to incorrect operation. The invention utilises a property of the impedance matching network which can also be seen from Figure 2 This property is that, so long as the value of L, brings operation within what may be termed the " region of reversal" (i e in the area RR of the circle between the radii RR 1 and RR 2) vector Ra/ZL is over 0 5 and the input impedance is always substantially less than the required load, assumed, for the sake of example, to be 50 ohms (The values of aerial resistance that would normally be matched by the network must be below 2 RI, i e 25 ohms If above this they are in practice effectively reduced by adding capacity in parallel with the aerial in the usual way) Suppose, for

example, that the range of the vector over the region of reversal Ra IZL is from 0 5 to 1 2 so that if the aerial resistance is 10 ohms the input impedance varies from Ra I O 5 = 20 ohms to Ra/1 2 = 8 4 ohms-both well below the 50 ohms load required If, therefore, the arrangement is made such that, so long as the input impedance is below a predetermined value (for example 45 ohms) such that operation is taking place in the region of reversal, the direction of rotation of the tuning control motor as determined by the phase discriminator is reversed, the said motor will run in the direction to take the tuning outside the region of reversal back into the proper region and, when in consequence the input impedance rises above the said predetermined value, the phase discriminator will once more alone determine the direction of motor travel as in the ordinary 70 way. According to this invention, therefore, an automatic control system for an impedance matching network having at least two adjustable elements, one for tuning control and the 75 other for impedance matching control, comnprises two impedance comparators and a phase discriminator, adjustment means for each ok said elements, means controlled by said phase discriminator for adjusting the adjustment 80 means for the tuning control element in response to departures from the resonant condition and in a direction to restore said condition, means controlled by one impedance comparator for adjusting the adjustment means 85 for the matching control in response to departures from the matched condition and in a direction to restore said matched condition, and means controlled by the other impedance comparator in response to the occurrence of 90 an input impedance of said network below a predetermined value which is substantially less than that for the matched condition, for reversing the direction of adjustment of the tuning control element as determined by the phase 95 discriminator. Figure 3 is a highly simplified block diagramn drawn in the same manner as the block diagram of Figure 1 but sho-wing an embodiment of this invention The inductances L, 100 and L, are adjusted respectively by the motors MA and MB as in Figure 1 and these motors are respectively controlled by a phase discriminator A and an impedance comparator B In addition, however, there is 105 provided another impedance comparator C, the output of which, after amplification in a suitable D C amplifier D controls a relay E having contacts which can introduce a reversal of the direction of rotation of the motor MA 110 with respect to the direction that would otherwise be produced by the phase discriminator A When the impedance conditions in the timed circuit are such that the signal obtained from the discriminator would produce a rota 115 tion of the tuning control LS in the undesired direction The impedance comparator C is so adjusted that if the input

impedance is below a predetermined value, that is to say if the input impedance is at a value corre 120 sponding to operation in the region of reversal, the relay E is operated so as to override as regards direction of running of the motor MA, the direction control imposed by the phase discriminator A Accordingly the said motor will 125 adjust the inductance L, to bring the apparatus back into the required region of operation whereupon the relay E will release and the phase discriminator A take direct charge in the normal way 130 785,838 Figure 4 shows the arrangement of Figure 3 in more detail In Figure 4 the load is shown as an aerial RA and the two impedance comparators C, B of Figure 3 are shown within the correspondingly marked chain line blocks. These devices are as known per se and require no specific description herein The output of the phase discriminator A is fed along lead AO and after amplification in a D C amplifier comprising valves 1 2, 3 and 4 operates one or other of two relays 5 and 6 in dependence upon whether the tuning adjustment at the moment is one giving a lagging phase angle or a leading phase angle The relays 5, 6 operate in effect as reversing relays for the motor MA controlling the polarity of the energisation thereof in a manner which will be obvious from the diagram It will be noted, however, that the control circuit for the motor MA includes a relay E and that in one position of the relay E operation of relay 5 will produce rotation of the motor MA in one direction, while in the other position of the relay E operation of relay S will be effective While relay E is in this other position it will produce rotation of MA in the opposite direction The relay E will not reverse the direction of rotation produced by operation of the relay 6 because the operation of relay 6 ensures that the motor is rotating in the desired direction The relay E is actuated by the output from the first impedance comparator C taken along the lead CO and amplified in a D C amplifier D including the valves 7, 8 The impedance comparator C is so adjusted that if the input impedance is below a predetermined minimum such that the region of reversal has been entered the motor MA will be run in a direction to adjust the inductance L, to a value which brings the input impedance above that predetermined minimum The impedance comparator B effects control of the inductance L, by means of the motor MB in manner known per se, the said output being taken via lead BC and after amplification in D C amplifiers comprising the yalves 9, 10, 11 and 12 employed to operate one or other of two relays 13, 14 controlling the polarity of energisation of the motor MB.

* Sitemap * Accessibility

* Legal notice * Terms of use * Last updated: 08.04.2015 * Worldwide Database * 5.8.23.4; 93p