US3025879A - Hydro-electric servo mechanisms - Google Patents

Description

March 20, 1962 Filed Oct. 12, 1959 J. FAISANDIER HYDROELECTRIC SERVO MECHANISMS 2 SheetsSheet 1 ZZZ/U 6121121 7. Fa/LoaR/dzLer March 20, 1962 J. FAISANDIER 3,025,879

HYDROELECTRIC SERVO MECHANISMS Filed Oct. 12, 1959 2 Sheets-Sheet 2 N INVENTOR.

Julia r, and 6 8.2"

HTTYJ.

3,025,879 HYDRO-ELECTRIC SERVE MECHANISMS Jacques Faisandier, 32 Blvd. Felix Faure,

Chatillomsous-Eagneux, France Filed 9st. 12, 1959, Ser. No. 845,829 (Ilaims priority, application France Oct. 17, 1958 Claims. (Cl. 137-623) This invention relates to hydro-electric servo mechanisms and may be considered as an improvement of my copending application Serial No. 797,654, which is in cluded herewith by way of reference. In this pending application I disclosed the use of torque motors, more particularly torque motors coupled with a damping generator, in hydro-electric servo controls in which the final position of the hydraulic device is defined by a control voltage, known as the input voltage, the output movement of the hydraulic device being marked by an output voltage providing the feed back possibly in combination with one or more damping voltages, in particular voltages marking the acceleration and speed, respectively, of the input or output movement.

I have now made various improvements in this device.

According to a first improvement it is proposed to correct the influence of the leakage flux which is created between the torque motor and the damping generator, and which gives rise to a voltage which is not proportional to the speed.

According to a second improvement use is made of a control device for the torque motor which allows a reduced current consumption, whilst maintaining the absence of time constant of the conventional connecting systems with continuous consumption.

In the examples of the copending application, which does not comprise the said control device, only an amplifier is provided, said amplifier receiving the input signal in the form of direct voltage and being directly connected to the coil of the torque motor. Such an elementary system of wiring has the disadvantage of causing a drift, that is to say for a zero input voltage the output voltage fluctuates very slowly around zero.

It is already known to overcome this disadvantage by a conventional method, which consists in modulating the direct control current at the input, by selecting a carrier current of suitable frequency, and then demodulating at the output of the amplifier before connecting up with the torque motor.

One of the disadvantages of this arrangement is that it requires a considerable and continuous current consumption.

For example, in the case of a conventional ring demodulator, one finds that the resistances of the ring must be of the order of the resistance of the coil of the torque motor. In consequence, the polarisation voltage must likewise be of the order of magnitude of the control voltage and under these conditions, even in the absence of a signal, the power consumed by the ring resistances, which are still subjected to the polarisation voltage, is quite considerable.

This continuous consumption can be avoided by using a polarised amplifier, functioning as class C (continuous direct voltage), and by placing two windings instead of one on the torque motor or, which amounts to the same thing, using one winding with a middle point.

Such a connection has been shown in FIGURE 2. Although this connection is known, a brief description thereof will facilitate understanding of the invention, by comparison.

In this figure which is really a simplified diagram, 50' designates the polarised alternating amplifier, 51 the torque motor coil with middle point, 52 the transformer, the primary of which is in series with the source, not

ent

shown, supplying the polarisation carrier current, 53' is a transformer at the output of the amplifier, the middle point of the secondary 54 of this transformer being earthed. 56' and 5'7 are two valves, the cathodes of which are subjected to a negative voltage and the plate circuits of which are in series with the windings 51 and 5'4. As can be seen, the valves are supplied with positive voltage only half the time which may cause half a periods delay, which in certain cases can be harmful.

In this diagram the other parts of the servo control, which are not indispensable to this explanation, have not been shown. If necessary reference can be made to FIC- URES 2 or 4 of the copending application.

The object of the invention is to obtain, on the one hand, the low consumption of the preceding wiring and, on the other hand, the absence of time constant of continuous consumption systems.

According to the invention, a phase demodulator is used, that is to say the alternating voltage of the ampli-' fied signal is injected, as in the foregoing case, in antiphase into the grids of two electronic tubes mounted in opposition while an alternating voltage is applied in phase to the two plates, the voltage being applied to the plates in the form of two unidirectional currents obtained from the same rectified alternating voltage, these two unidirectional currents being injected in opposition at two opposite vertices of a ring constituted by four identical impedances, the two other vertices being connected to the plates. This arrangement ensures that there is always one plate subjected to a positive voltage. v

The non-adjacent windings of the ring are associated so as to constitute the primaries of two transformers, each transformer comprising two secondaries, the voltage of which is rectified in order to supply two unidirectional currents having the same direction, each group of two unidirectional currents being injected into a coil of the torque motor, in such a manner that the direction of each of the said unidirectional currents is independent of the alternation of the alternating voltage, and depends solely on the dephasing through which corresponds to the reversal of the input signal.

For each of the improvements, one embodiment of the inventive idea showing other advantages of the invention will be described hereunder, the scope of the invention not being limited to or restricted by the specific features of the examples chosen for illustration.

In the accompanying drawings:

FIGURE 1 shows a diagram of connections for eliminating eddy currents due to the leakage flux.

FIGURE 2 shows, as already stated, a phase demodu- In FIGURE 1 the same references have been used as in FIGURE 1 of the copending application. 5 is the torque motor with its armature 1, winding 2 and rotor 3. The unit 9 is the damping generator, with its armature 8, its rotor 6 mounted on the shaft 4 which it has in common with the torque motor, and the winding 7.

On the armature l is disposed a second Winding 45 in series with the winding 7, the windings 2 and 45 being in opposite directions, so that the fiuxm are in opposition.

The potentiometer 46 allows the corrective current to be regulated.

The reverse arrangement is also possible, that is to say placing the compensating winding on the armature 8, in

primariesof the transformers, while the secondaries'and the entire circuit connected to the secondaries are shown in FIGURE 4.

The alternating voltage or polarisation carrier current is supplied by'the transformer 60, the primary of which is connected by its terminals 61, 62 to a high voltage source, for example the mains. The secondary 63 is constituted by two separate windings or a single winding having an earthed middle point, as shown.

The rectifiers 64,- 65 eliminate the negative alternations and inject a unidirectional current at the two vertices 66, 67 of the ring 68, the two other vertices 69, 74) of which are :connected to the'plates of the two tubes 56, 57, respectively.

Owing to this system of connections, it can be seen at once that there is always one plate under positive voltage and the possibility of delay inherent in the connection shown in FIGURE 2 is eliminated. I

In FIGURE 4 the four primaries 70, 66 and 67, 69 belonging to the transformer 80, and 70 67 and 66, 69 belonging to the transformer 81 have been shown, these primaries being separated graphically for convenience of illustration. The transformer 80 has a secondary 32 with an earthed middle point, and the transformer 81 has a secondary 83 with earthed middle point.

92 93 are the two coils of the torque motor, the directions ofwinding of which are reversed, and the terminals ofv which are designated 84, 85, the two other terminals being earthed. v

To theterminals of the secondary 83 are connected the rectifieI 8 6, 88 which inject a unidirectional current through the terminal 84.

To the terminals of the secondary 82 are connected the rectifiers 87, 8-9 which inject a unidirectional current through the terminal 85, this current being'in opposition to the preceding unidirectional current.

Operation is as follows:

If the grid voltage of the tube 56 is in phase with its.

plate voltage, the grid voltage of the tube 57 is in antiphase with its plate voltage. The anodic current of the tube 56 is therefore greater than that of the tube 57, the terminal 70' being more positive than the terminal 69, this being the more marked, the greater the amplified signal.

In this ,case it is clear that the alternation of the voltage at the mains voltage does not change the direction of the flux in the Winding 2;

In effect, according to, one alternation the current passes in the direction 66, 70 and the unidirectional current is injected through the vterminalSatinto the winding 92- according to the other alternationsthe current passes in the direction 67, 70 and the unidirectional current is injected through the terminal 85 into the Winding 93;

If the amplified signal undergoes a 180 dephasing owing to the reversal of the input signal, the polarity of the terminals 70 and 69 is reversed. In this case the current passes in the direction 66,69 on one alternation and in the direction 67, 69 on the other alternation. In the'first case the unidirectional current is injected into the winding 93 through the terminal 85 and in the second case into the winding 92 through the terminal 84. The alternation therefore has no effect.

Between the two windings 9-2, 93 and earth a small resistance 90 is provided.

Across this resistance, at 91, it is possible to provide a voltage which is applied to the amplifer 50 to obtain a negative feed back, this voltage being proportional to the intensity of the current passing through the resistance 90.

This negative feedback makes it possible to regulate thevalue of the torque and thus to improve the characteristics of the servo-mechanism, in particular to reduce the time constant while maintaining the advantages of damp- The connection which has just been described may be carried into effect by replacing the tubes 56, 57 by transistors. In this case it is sufricient to reverse the direction of the rectifiers 64, 65. The permanent consumption may thus be lowered to 2 watts, for example, for a maximum output power of 10 watts. 7

It should be noted that the diagrams show only those parts of the apparatus necessary to the understanding of the invention. In particular the conventional devices, such as the cathode-heating circuits, filters, regulating impedances, etc. have been omitted. I

The schematic of FIG. 5 includes the hydroelectric servo mechanism such as shown in FIG. 4 of the abovementioned copending application, together with the circuits of FIGS. 3 and 4 substituted for the amplifier 11 shown in that application. The input signal is mechanically applied by rotary movement imparted to the shaft 30 on which is mounted the rotor of the deviation indicator 20E which supplies the input circuit 10 with an alternating voltage which is proportional to the deviation angle imparted thereto.

The deviation indicator 20S supplies the circuit 32 with an alternating voltage marking the output movement. For

this purpose a rack 33 moved by the valve 14 rotates the rotor of the indicator 205 through an angle proportional to the extent of the output movement through the pinion 34 and the shaft 35.

On the shaft 4 of the torque motor is keyed the rotor of another deviation indicator 20A which supplies the circuit 36 with an a dditional damping voltage which introduces the element jgd! while the generator 9 provid es the element g. dt

S being a variable defining'the output movement. The use of such an additional damping, voltage is known but it is usually supplied by. a potentiometer. Finally, there can then be introduced at the input, for example at 37, an additionalvoltage proportional to the speed of the input movement, which is likewise known per se and makes it possible to correct, for a given frequency range, the deviation proportional to the input speed which is introduced by'the servo mechanism between the input and the output and which is an indispensable condition of stability. The introduction of this additional voltage is effected by a generator 38 keyed to the shaft 30 and supplying a direct voltage proportional to the input speed.

What I claim is:

1. In a hydraulic servo-control system having a movable distributor for controlling a hydraulic device, an electric torque motor for operating the distributor and having two control windings, the directions of which are reversed, means for applying A.C. control signals to said windings comprising an amplifier operating in class C and including a pair of electron discharge tubes, each having a control electrode, an electron emitter and a collector electrode, means for applying the control signals to the control electrodes in opposite phase with respect to a reference potential, four transformers, each having a primary and a secondary winding, the four primaries connected to form a ring having four vertices, two opposite vertices being each connected between the collector electrodes, a source of AC. voltage, means connected to said source for applying a unidirectional voltage of the same polarity to the two other opposite vertices respectively, and means for rectifying the output from each of the secondary windings, the secondary windings corresponding to two opposite primary windings applying a voltage of the same polarity to one of the control windings of the motor, the two other secondary windings applying a voltage of inverse polarity to the other one of the control windings of the motor.

2. In a hydroelectric servo-control system having a movable distributor for controlling a hydraulic device, an electric torque motor for operating the distributor and having a pair of control windings wound in opposite directions, means for supplying alternating current signals to the windings comprising a push-pull amplifier operating in class C and including a pair of electron discharge devices each having a control electrode, an electron emitter electrode and a collector electrode, means for applying control signals to the control electrodes in opposite phase with respect to a reference potential, a pair of transformers each having a pair of primary windings and a secondary winding, the primary windings being connected in the form of a bridge network with the primary windings of the respective transformers in opposite arms of the network, the collector electrodes being connected across two vertices of the network, an alternating current source, means connected to the source for applying a unidirectional potential of like polarity to the remaining opposite vertices of the network, and means for rectifying the output from each of the secondary windings in relatively opposite polarities and applying the rectified outputs to a respective one of the motor control windings.

3. In a hydroelectric servo-control system as defined by claim 2 in which the alternating current source comprises a source of balanced potential, a like poled rectifier between each terminal of the source and the respective remaining opposite vertices of the network.

4. In a hydroelectric servo-control system as defined by claim 2 in which the means for rectifying the output from each of the secondary windings in relatively opposite polarities and applying the rectified outputs to a respective one of the motor control windings includes a pair of like poled rectifiers connecting the terminals of each secondary, one terminal of each motor control windings being connected to the junction of a respective pair of rectifiers, and the other terminal of each motor control windings being connected to the midpoint of a respective secondary Winding.

5. In a hydroelectric servo-control system as defined by claim 4 in which the midpoints of the secondary windings are connected together and the other terminals of the motor control windings are connected in common to the midpoints of the secondary windings through a resistance.

References Cited in the file of this patent UNITED STATES PATENTS 2,040,014 Moseley May 5, 1936 2,398,421 Frische et a1 Apr. 16, 1946 2,466,041 Peoples et al. Apr. 5, 1949 2,615,658 Young Oct. 28, 1952 2,710,933 Dion June 14, 1955

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