Electronic Device for Multiplexing Several Loads Excited by Alternating Current

1. Field of the Invention

The present invention relates to the sequential excitation of several loads with the aid of an alternating current.

2. Discussion of the Background

This problem is posed especially in the electromagnetic systems for locating the position and orientation of an object at short range, such as those systems used for locating the position and the orientation of a helmet worn by a pilot, with respect to a three-axis reference system related to the pilot's cockpit, so as to allow the operation of certain instruments with the aid of the movements of the head pilot while leaving him complete freedom of movement.

One way, by an electromagnetic route, of locating the position and the orientation of an object, at short range, consists in sending at one reference point, successively along the three axes of an absolute three-axis reference system, electromagnetic fields at low frequency of the order of 10 KHz, in measuring, along the three axes of a relative three-axis reference system related to the object whose position and orientation it is desired to know, the components received from the successive electromagnetic fields sent along the three axes of the absolute three-axis reference system, and in deducing, from these measurements and from a preliminary cartography, the position and orientation of the relative three-axis reference system and hence of the object with respect to the absolute three-axis reference system. This way of doing it functions all the better when it is possible to generate successive electromagnetic fields in the precise directions of the three axes of the absolute three-axis reference system, that is to say when the successive emissions of these three electromagnetic fields are capable of being well decoupled.

The successive sending of these three electromagnetic fields is done with the aid of a triple antenna placed at the reference point and shaped into a cube with faces parallel to those of the absolute three-axis reference system. This triple antenna consists of three double orthogonal windings each arranged along two parallel faces of the cube and dimensioned so as to generate, for the same excitation current, the same electromagnetic field intensity outside the cube. Reception is done with the aid of a triple antenna of the same type carried by the object whose position and orientation it is desired to know, and shaped into a cube whose faces are parallel to those of the relative three-axis reference system.

The triple sending antenna constitutes, for the sender, a triple inductive load having a certain number of specific features.

Its three double windings, when they have the excitation current passing through them, develop, at their terminals, a high voltage which reaches about a hundred volts, pushing up the cost of the transistor multiplexer in the case where the transistors would have to withstand this voltage directly.

Moreover, these three double windings are not identical by reason of the constraints on coil forming along the faces of a cube, and exhibit different impedances which does not make it easy to maintain the same excitation current strength.

Moreover, these three windings are coupled by mutual inductance which promotes leakage currents.

The object of the present invention is to combat the above mentioned difficulties so as to carry out, in a simple way and at low cost, a multiplexing which is adapted to the specific features of a triple sending antenna of an electromagnetic system for locating the position and the orientation of an object at short range.

Its subject is an electronic device for multi-plexing loads to the terminals of a source of alternating electrical energy, including:

means for coupling the source of alternating electrical energy by electromagnetic flux to the loads including at least one primary excitation winding connected to the terminals of the source of alternating electrical energy, and secondary windings, equal in number to that of the loads, at least partially coupled to the primary excitation winding and each connected to the terminals of a load;

means of inhibiting the means of coupling by electromagnetic flux including auxiliary windings, equal in number to that of the loads, each totally coupled with one of the secondary windings; and

means for control of the inhibition means imposing the inhibition of all the magnetic couplings except one, which changes depending on the load to be connected to the source of alternating electrical energy.

The means of coupling by electromagnetic flux may include one or more primary excitation windings. When the primary excitation winding is a single one, it is partially coupled to the various secondary windings within a single transformer having a magnetic circuit with several parallel legs, a first leg around which is wound the primary excitation winding and other legs around each of which are wound both a secondary winding and an auxiliary winding of the inhibition means. When the means of coupling by electromagnetic flux include several primary excitation windings, the latter are equal in number to that of the loads, connected in series to the terminals of the source of alternating electrical energy and each totally coupled with a secondary winding within an individual transformer which also includes an auxiliary winding of the inhibition means.

The inhibition of the coupling by electromagnetic flux is obtained in the case of several primary excitation windings with separate transformers either by short-circuiting the auxiliary windings or by making a direct current pass through them, giving rise to saturation.

Advantageously, the electronic multiplexing device further includes isolating switch means equal in number to that of the loads each interposed in series between a load and the secondary winding to which it is connected, the control means imposing a closed state on the isolating switch means arranged in series with the load whose coupling by electromagnetic flux with the source of alternating electronic energy is not inhibited and an open state on all the other isolating switch means.

Other characteristics and advantages of the invention will emerge from the following description of an embodiment given by way of example. This description will be given with regard to the drawing in which:

FIG. 1 represents the electrical diagram of a circuit for excitation of the double windings of a triple sending antenna of an electromagnetic locating system including an electronic multiplexing device according to the invention provided with means of coupling by electromagnetic flux incorporating several transformers;

FIG. 2 represents a skeleton diagramme of a T switch making it possible to connect or to disconnect a load and a source while, by comparison with a simple switch, improving the isolation of the load with respect to the source when it is in the open state;

FIGS. 3 and 4 illustrates, seen from above and seen from the side, the magnetic circuit with several parallel legs of a single transformer which can be used for the means of coupling by electromagnetic flux; and

FIG. 5 shows the modification of the electrical diagram of FIG. 1 entailed by the use of the single transformer, the magnetic circuit of which is shown in FIGS. 3 and 4.

In FIG. 1 can be seen the two parts 1, 1', 2, 2', and 3, 3', of the three double windings of a triple sending antenna of an electromagnetic system for locating the position and orientation of an object, at short range. These double windings are, as mentioned previously, arranged in orthogonal planes. They are intended, on the one hand, to be excited successively by an alternating current of the same intensity, with a frequency of the order of about 10 kilohertz, although they do not present exactly the same impedance, and, on the other hand, when they are not excited, to have residual currents which are as weak as possible passing through them.

The alternating excitation current is delivered sequentially to the double windings of the triple antenna, by means of a multiplexer according to the invention, by means of an amplifier 4 equipped with a current slaving loop common to the three double windings.

The two parts 1, 1', 2, 2' or 3, 3' of each of the three double windings are connected in series and their interconnection point taken to ground. Two current measurement resistors 5, 5', of low value, for example one Ohm, are interposed in series between the two parts of each of the double windings, on either side of the earth. They deliver, to the input of the current slaving loop, an alternating voltage proportional to the strength of the alternating excitation current actually passing through the double windings. The measurement amplifier 6 of the current slaving loop amplifies this measurement voltage and applies it to the amplifier 4 which compares it with an input datum alternating voltage Ve and adapts the amplitude of its alternating output voltage in order to cancel out the error between measurement voltage and datum voltage, and to act so that the alternating excitation current keeps a constant strength in the double windings.

The multiplexer interconnecting the three double windings, 1, 1', 2, 2', and 3, 3' to the output of the amplifier 4 includes three transformers 7, 8 and 9, as many as there are double windings, each provided with a primary winding 71, 81, 91 with intermediate tappings, with a secondary winding 72 with intermediate tappings and with a short-circuiting winding 73.

The three primary windings 71, 81, 91 of the transformers 7, 8 and 9 are connected in series, via a tuning capacitor 10, between the output of the amplifier 4 and ground.

The secondary winding 72 of the first transformer 7 is connected to the terminals of the first double winding 1, 1' of the triple antenna, while the secondary winding of the second transformer 8 is connected to the terminals of the second double winding 2, 2' of the triple antenna and the secondary winding of the third transformer 9 is connected to the terminals of the third double winding 3, 3' of the triple antenna.

The three auxiliary short-circuiting windings 73 of the transformers 7, 8, 9 are closed by a first bank of three switches controlled by a control circuit 40. Each of these switches is formed by two field-effect transistors 74, 75 interconnected by their source electrodes placed at ground potential. The drain-source junctions of these field-effect transistors 74, 75 are placed in series and in opposition at the terminals of the auxiliary short-circuiting winding so as to allow the blocking of the two current half-cycles. Their gate electrodes are connected in parallel and receive, from the control circuit 40, a blockage or saturation control voltage C1, C2, C3. This control voltage is a gate-source bias voltage which is not floating with respect to earth due to the fact that the transistors have their source electrode at earth potential, which is made possible by the isolation of the auxiliary short-circuiting winding with respect to the other primary and secondary windings of each transformer.

A second bank of three controlled switches allows the secondary circuits of the three transformers 7, 8, 9 to be opened in order to reduce the leakage currents. Each controlled switch of this second bank is formed by two field-effect transistors 11, 12; 21, 22; 31, 32 interposed in series between the two parts 1, 1'; 2, 2'; 3, 3' of a double winding of the triple antenna, on either side of the measurement resistors 5, 5'. The source electrodes of these field-effect transistors are connected to earth via the measurement resistors 5, 5' and are thus at a low potential with respect to earth. Their drain-source junctions are then placed in series and in opposition in the secondary circuit of a transformer, which allows the blocking of the two half-cycles of the current. Their gate electrodes are connected in parallel and receive, from the control circuit 40, a blocking or saturation control voltage. As the field-effect transistors 11, 12; 21, 22; 31, 33 have their source electrode at a potential close to earth, this control voltage is a gate-source bias voltage which is not floating with respect to ground which, conveniently, takes the same values as the control voltage of the transistors of the first bank of switches. More precisely, the control voltages of the field-effect transistors 11, 12; 21, 22; 31, 32 of this second bank of switches take values C1, C2, C3 opposite to those applied to the field-effect transistors of the first bank of switches so that the switches of the second bank take states opposite to those of the first bank.

It can be envisaged, in the case in which the current slaving loop is not indispensable, to omit it and to replace the measurement resistors 5, 5' by conducting bridges. The field-effect transistors of the controlled switches of the second bank will then all be connected to ground by their source electrode.

In normal operation, the control circuit 40 gives rise to the blocking, each in turn, of one of the three switches of the first bank enclosing the auxiliary, short-circuiting windings of the three transformers 7, 8 and 9, the conduction of the other two switches of the first bank and the placing of the switches of the second bank into opposite conduction states. The two transformers which have their short-circuiting winding closed by a switch of the first bank in conduction saturate. They reflect very low impedances at their primary and secondary. It results therefrom that the double windings of the triple antenna would be practically in short-circuit if they were not opened by the corresponding switches of the second bank. Moreover, a negligible voltage drop is produced at their primary transferring the majority of the alternating excitation voltage seen at the output of the amplifier 4 by the tuning capacitor 10 to the terminals of the primary of the third transformer whose auxiliary short-circuiting winding is opened by a turned-off switch. As, moreover, this third transformer has its secondary circuit closed at the terminals of a double winding of the triple antenna by means of a switch of the second bank in the conducting state, it delivers to this double winding an alternating excitation current which keeps a constant strength under the action of the current slaving loop.

The use of a primary' winding with intermediate tappings for each transformer gives the possibility of impedance matching. It is thus possible, by a judicious choice of the tappings by which the primary windings of the transformers are driven, to make it such that the double windings, although of different impedances, reflect identical impedances to the primaries of the transformers when the latter are not saturated.

The use of the two banks of controlled switches in order, at the same time, to short-circuit the extremities of the non-excited double windings of the triple antenna and to open them at a mid point allows a much better cancellation of the currents which pass through them to be obtained. In effect, the switches of the two banks behave, for each winding, like the mounting of switches in a T of FIG. 2 which exhibits, between a source 50 of alternating electrical energy and a load 51, two switches in series K1 and K3, operated in synchronism and completed by a third switch K2 which links the earth to their mid point and which is operated in opposition. Such a mounting makes it possible, as is well known, to reduce the effects of the parasitic capacitance presented by the field-effect transistors used for the switches since, when the load is isolated from the source by the opening of the switches K1, K3 and by the closing of the switch K2, there is, upstream of the switch K3 in series with the load, only a very small portion of the voltage from the source. The switch of the first bank which is placed at the terminals of the auxiliary, short-circuiting winding of a transformer and controls the saturation of the latter, plays the part of the switches K1, K2 while the switch of the second bank interposed in series with the load plays the part of the switch K3.

The use of transformers between the output of the amplifier 4 and the double windings 1, 1'; 2, 2'; 3, 3' of the triple antenna makes it possible to obtain a first voltage gain by acting on the ratio between primary and secondary windings. This first voltage gain is completed by a second voltage gain resulting from the placing of the inductive load of the amplifier 4 into resonance by means of the linking capacitor 10, this complement being a function of the overvoltage factor of the oscillating circuit obtained which may reach four or five.

As can be seen in FIG. 1, the intermediate tappings of the secondary winding of each transformer are connected to one of the extremities of a double winding of the triple antenna by means of a selector 76 which makes it possible to change the tuning frequency of the load of the amplifier 4 by changing the self inductance seen at the primary of the transformer. It may, in fact, be useful, in the case in question of an electromagnetic system for locating the position and the orientation of an object at short range, to modify the operating frequency in order to get away from another electromagnetic locating system operating in the vicinity at the same frequency.

The three transformers 7, 8 and 9 used in the diagram of FIG. 1 may be replaced by a single transformer with a single primary winding which it makes it possible to reduce the ohmic losses in the primary circuit. The single transformer then exhibits a magnetic circuit with four parallel legs around which are distributed the coils. This magnetic circuit may be produced, as represented in FIGS. 3 and 4 with the aid of four pillars or legs 100, 101, 102, 103 of the same length held between two plane yokes 104, 105 of triangular profile. The central leg 100 receives the single primary winding while each peripheral leg 101, 102, 103 receives a secondary winding and an auxiliary, short-circuiting winding.

The magnetic flux generated by the primary winding in the central leg 100 of the magnetic circuit is closed by the yokes 104 and 105 and by the single peripheral leg 101, 102 or 103 which does not have its auxiliary winding in short-circuit, so that only the secondary winding of this peripheral leg is coupled to the primary winding which carries out the multiplexing function.

The partial diagram of FIG. 5 shows the modifications which result for the diagram of FIG. 1 from the use of a single transformer with a magnetic circuit with several parallel legs.

The output of the amplifier 4 is now connected by the use of the tuning capacitor 10 to the single primary winding 110 coiled round the central leg 100 of the transformer. The secondary windings 111, 112 and 113 respectively each coiled round a peripheral leg 101, 102 and 103 respectively of the transformer with an auxiliary winding 121, 122 and 123 respectively are connected, as before, to the extremities of the three double windings of the triple antenna via a selector 76 making it possible to change the tuning frequency of the load of the amplifier 4.

The counter-balance related to the singleness of the primary is the necessity of using secondary windings with different numbers of turns for balancing the impedances in the case in which the loads exhibit different impedances. With this aim, it is possible to make provision to equip the two extremities of each secondary winding with a set of intermediate tappings, one intended for the selector making it possible to change the tuning frequency and the other intended for balancing the impedances of the different loads.

It is possible without departing from the context of the invention, to modify certain arrangements or replace certain means by equivalent means. Thus, in particular, in the case of the embodiment with several separate transformers, one per load, it is possible, in order to suppress coupling by magnetic flux, not to short-circuit an auxiliary winding but to cause a direct current of sufficient strength to saturate the magnetic path to pass through it.