EP0131760B1 - Control apparatus for two bidirectional step motors - Google Patents

Abstract

The device includes two driving circuit (C1, C2) each of which includes six power transistors (T11-T16, T21-T26) that are connected in pairs into three parallel circuit branches. A first coil (B11) of one of the motors and a first coil (B21) of the other are, on the one hand, both connected to the junctions of the transistors of one of the branches of one of the driving circuits (C1) and, on the other hand, respectively connected to the junctions of the transistors of the two other branches of this circuit. The same applies for the second coils (B12, B22) of the motors and the other driving circuit (C2). The various transistors are controlled so that the two coils of the same motor simultaneously receive the current pulses which are needed to make it turn but by preventing the simultaneous application of current pulses to a coil from one of the motors and to a coil from the other. This arrangement makes it possible to save four transistors and two output terminals on the integrated circuit used to control the motors.

Description

The present invention relates to a device for controlling two bidirectional stepping motors of an electronic timepiece, which each have two coils.

This device can be used in particular in an analog watch.

It may be necessary to equip a watch with two stepping motors for various reasons, for example to increase the number of functions it can perform or of indications it can provide compared to a watch with a single motor having the same indicating members, or for allowing both electronic and rapid correction of the information it displays, or for both at the same time.

The use of two motors can sometimes even be justified by the simple fact that it makes it possible to produce a watch having the same functions as another, with a single motor, but by simpler means both in their construction and in their use.

For example, watches are known in which a first motor actuates a second hand and a minute hand while a second motor drives an hour hand and a date indicator. Such an arrangement allows both rapid setting of the time, easy change of time zone and easy incorporation into the watch of a chronograph function.

This solution even has another advantage: the energy consumption is significantly lower than if the watch had only one motor powered by motor pulses of fixed duration. Indeed, the motor which only drives needles and which, therefore, is always subjected to a low load, can be powered by low energy drive pulses. On the other hand, the motor which activates the calendar mechanism needs significantly more energetic pulses, but in much lower number, for example a dozen per hour. This therefore makes it possible to increase the life of the battery or to reduce its dimensions.

It is also known, for a watch which has only the usual three hands, to train that of the seconds on the one hand and those of the minutes and hours on the other hand. The latter two can then be used to set and display an alarm time on command, while the second hand is used to indicate by a particular movement that the time displayed is that of alarm.

Whether to allow faster correction of the information provided by the watch or so that the hands can take the shortest way to go from one position to another when they are used to indicate something other than the current time, it is always preferable to provide motor systems capable of operating in both directions.

There are currently several possibilities in the watchmaking field for producing a bidirectional motor system. One solution consists in continuing to use a conventional single-phase motor, of the Lavet type for example, which is designed to rotate only in one direction, and in adding to it a control circuit capable of producing and applying adequate motor impulses to it. to rotate it back and forth.

Another possibility is to use a stepping motor specially designed to rotate in both directions and in particular a motor with two coils.

However, the use of such motors poses problems, especially when it comes to including several in the same watch. Indeed, in most cases the design of the motor requires that the two coils be excited in turn to cause the rotation of the rotor in one direction or the other. Each coil must therefore be dimensioned so as to supply, on its own, the energy necessary for this rotation, that is to say that each coil must have practically the same volume as that of a stepping motor. classic with only one direction of rotation. On the other hand, there are motors like the one described in German patent application No. 3 026 004, the two coils of which can be excited simultaneously and contribute together to the formation of the magnetic field creating the torque which is applied to the rotor. Therefore, the total volume of the coils can be significantly reduced compared to that of coils supplied alternately and be almost equal to that of the single coil of a motor with a single direction of rotation.

However, the simultaneous supply of the two coils implies that the direction of current flowing in one of them is reversed approximately in the middle of the driving pulse applied to it. The motor control circuit must therefore necessarily comprise eight power transistors conventionally forming two bridges of four transistors, into which the two coils are connected respectively. For a watch with two motors this number of transistors should normally be multiplied by two. This is a drawback because it is well known that, unlike the logic circuits which control them, the power transistors occupy a large area on the wafer of the integrated circuit of the watch.

The use of motors whose coils are energized alternately is, in this respect, more advantageous because, as indicated in Swiss patent no. 632 128 or in application WOA8 101 205, it is then possible to provide only six transistors to supply the two coils of a motor. In addition, the number of integrated circuit output terminals reserved for supplying the coils can be reduced to three per motor instead of four. However, it is always desirable to limit the number of terminals of an integrated circuit as much as possible in order to improve its reliability and reduce its cost price.

The object of the present invention is to provide a control device for two stepping motors. bidirectional with two coils making it possible to simultaneously supply the two coils of the same motor with a reduced number of power transistors and to limit the number of terminals of the circuit in which these transistors are integrated with the electronic components which serve to control them.

• - deux bornes d'alimentation entre lesquelles peut être branchée une source d'énergie électrique,
• - un premier circuit d'attaque comprenant trois branches de circuit connectées en parallèle entre les bornes d'alimentation et comprenant chacune deux transistors en série qui peuvent être commandés pour appliquer des impulsions de courant polarisées à une première bobine de l'un des moteurs et à une première bobine de l'autre moteur, ces premières bobines étant connectées, d'une part, toutes les deux au point de liaison des transistors de l'une des branches et, d'autre part, respectivement aux points de liaison des transistors des deux autres branches;
• - un second circuit d'attaque comportant également trois branches connectées en parallèle entre les bornes d'alimentation et comprenant chacune deux transistors en série qui peuvent être commandés pour appliquer des impulsions de courant polarisées aux secondes bobines des moteurs, ces secondes bobines étant connectées, d'une part, toutes les deux au point de liaison des transistors de l'une des branches de ce second circuit et, d'autre part, respectivement aux points de liaison des transistors des deux autres branches; et
• - des moyens pour appliquer séparément des signaux de commande à chaque transistor des premier et second circuits d'attaque de façon que les deux bobines d'un même moteur reçoivent simultanément les impulsions de courant nécessaires pour faire tourner ce moteur et de façon à éviter l'application simultanée d'impulsions de courant à une bobine de l'un des moteurs et à une bobine de l'autre.

This object is achieved thanks to the fact that the control device according to the invention comprises:

• - two supply terminals between which a source of electrical energy can be connected,
• a first drive circuit comprising three circuit branches connected in parallel between the supply terminals and each comprising two transistors in series which can be controlled to apply biased current pulses to a first coil of one of the motors, and to a first coil of the other motor, these first coils being connected, on the one hand, both at the connection point of the transistors of one of the branches and, on the other hand, respectively at the connection points of the transistors the other two branches;
• a second drive circuit also comprising three branches connected in parallel between the supply terminals and each comprising two transistors in series which can be controlled to apply biased current pulses to the second coils of the motors, these second coils being connected, on the one hand, both at the connection point of the transistors of one of the branches of this second circuit and, on the other hand, respectively at the connection points of the transistors of the two other branches; and
• means for separately applying control signals to each transistor of the first and second drive circuits so that the two coils of the same motor simultaneously receive the current pulses necessary to make this motor turn and so as to avoid 'simultaneous application of current pulses to a coil of one of the motors and to a coil of the other.

Before describing in detail a possible embodiment which will allow a better understanding of the invention, it should be noted that it has already been proposed in patent application JP-A-57-55795 to control two motors with two coils each using two driver circuits with six transistors and connecting their coils as we have just indicated but they were then unidirectional DC motors intended in particular for tape recorders, therefore very different from those concerned by the 'invention.

• ―la figure 1 est un schéma de circuit illustrant la forme d'exécution que l'on a choisi de décrire à titre d'exemple;
• ―la figure 2 est un diagramme montrant des impulsions de courant qui peuvent être utilisées pour commander deux moteurs tels que celui qui est décrit dans la demande de brevet allemand précitée et auquel le circuit de la figure 1 peut être associé; et
• ― la figure 3 représente, sous forme d'un schéma bloc, un circuit qui, dans le cas de l'application de l'invention à une montre électronique, peut être associé à celui de la figure 1 pour commander deux moteurs par des impulsions motrices telles que celles qui sont représentées sur la figure 2.

The following description refers to the attached drawing in which

• ― Figure 1 is a circuit diagram illustrating the embodiment that we have chosen to describe by way of example;
• ― Figure 2 is a diagram showing current pulses which can be used to control two motors such as that described in the aforementioned German patent application and with which the circuit of Figure 1 can be associated; and
• - Figure 3 shows, in the form of a block diagram, a circuit which, in the case of the application of the invention to an electronic watch, can be associated with that of Figure 1 to control two motors by pulses power cars such as those shown in Figure 2.

As shown in Figure 1, the control device according to the invention comprises two driving circuits Ci and C ₂ each comprising three branches connected in parallel between two supply terminals b ₁ and b ₂ which are respectively connected to the positive pole and at the negative pole of an electrical energy source P, for example a battery.

Each of the six branches is formed of two complementary MOS field effect transistors connected in series, the drains of these transistors being connected together and their respective sources connected to the supply terminals b ₁ and b ₂ . In FIG. 1, the P channel transistors bear the references T ₁₁ , T, ₃ , T ₁₅ for the first driving circuit Ci and T ₂₁ , T ₂₃ , T ₂₅ for the second circuit C ₂ . The N channel transistors are designated by T ₁₂ , T ₁₄ and T ₁₆ , on the one hand, and by T ₂₂ , T ₂₄ and T ₂₆ , on the other hand.

A first coil B ₁₁ of one of the stepping motors to be controlled is connected between the connection point of the drains of the transistors T ₁₁ and T ₁₂ and that of the drains of the transistors T ₁₅ and T ₁₆ , while a first coil B ₂₁ of the second motor is connected between the junction point of the drains of the transistors T ₁₅ and T, ₆ and that of the drains of the transistors T, ₃ and T ₁₄ . Similarly, the second coils B ₁₂ and B ₂₂ of the two motors are connected, on the one hand, both at the connection point between the transistors T ₂₅ and T ₂₆ and, on the other hand, respectively at the junctions between the transistors T ₂₁ and T ₂₂ and between the transistors T ₂₃ and T ₂₄ .

The motors to which the four coils B ₁₁ , B ₁₂ , B ₂₁ and B ₂₂ belong have not been shown in the drawing because they may in fact be any kind of bidirectional motors usable in a room. timepieces whose two coils can or must be supplied simultaneously and for which the direction of the current must be reversed at least once in one at least of the coils during the duration of the driving pulses. In addition, the two engines may be different.

The gates of the transistors T ₁₁ to T ₁₆ and T ₂₁ to T ₂₆ receive from a control circuit not shown in FIG. 1 but of which an example will be given later, control signals of duration and polarity defined so as to block or make the desired transistors conductive so that each of the motors rotates at the desired frequency and in the desired direction, while preventing the two motors from operating simultaneously.

To make the transistors T ₁₁ , T ₁₃ , T ₁₅ , T ₂₁ , T ₂₃ and T ₂₅ conductive, the control circuit must apply to the gate of each of these a logic signal "0". On the contrary, a logic signal "1" will block them. On the other hand, the control circuit must apply to the gates of the transistors T, ₂ , T ₁₄ , T ₁₆ , T ₂₂ , T ₂₄ and T ₂₆ a logic signal "0" to block these transistors and a logic signal "1" to make them conductive.

As is generally the case in logic circuits, here a logic signal "0" and respectively "1" means a signal having the same voltage as the negative pole, respectively positive, of the energy source P.

Furthermore, to pass a positive current through the coil B ₁₁ , respectively B ₁₂ , in the direction of the arrow designated by +, the control circuit must make the transistors T ₁₂ and T ₁₅ , respectively T ₂₂ and T, conductive. ₂₅ . On the contrary, to pass a negative current through these same coils, the control circuit must make the transistors T ₁₁ and T ₁₆ , T ₂₁ and T _{26 respectively} .

Likewise, for a positive current to flow in the coil B ₂₁ , respectively B ₂₂ , it will be necessary to make the transistors T ₁₄ and T ₁₅ , respectively T2 ₄ and T ₂₅ , conductive, whereas, to pass a negative current through these same coils, the transistors T ₁₃ and T ₁₆ , respectively T ₂₃ and T ₂₆ must be made conductive.

In addition, it may be useful, as in the case of a conventional unidirectional motor, to short-circuit for a certain time at least one of the coils of the motor which has just received driving pulses, in order to reduce the duration of the oscillations of the rotor around its equilibrium position. For this, the control circuit must make the two N-channel transistors or the two P-channel transistors conductive, to the drains to which the coil to be short-circuited is directly connected.

The device which has just been described therefore makes it possible to simultaneously control the coils of each of the motors in the same way as if the four coils were each connected in a bridge of four transistors, but using only twelve power transistors which occupy all substantially the same area on the integrated circuit and saving two output terminals for this circuit.

The only limitation is that the two motors cannot operate at the same time. In fact, this does not constitute a drawback, at least in the case of a watch where an offset of a few milliseconds between the movements of two hands which are not driven by the same motor is not a problem. On the contrary, even when it is possible to control two motors simultaneously, it is preferable not to do so because the current spikes that this would cause due to the relatively large consumption of the motors could disturb the proper functioning of the integrated circuit. In addition, there is a risk of there being a reciprocal influence from one motor to the other due to the magnetic fields created by the coils.

The diagram in FIG. 2 shows the shape of the current pulses that the driving circuits C, and C ₂ of FIG. 1 are caused to apply to the coils B ₁₁ , B ₁₂ , B ₂₁ and 8 ₂₂ when it acts to control two motors such as that described in the German patent application No. 3,026,004 cited above and which rotates in 180 ° steps. This diagram takes into account the choice which is made in this patent application for the positive and negative directions of the currents in the coils.

Part a of FIG. 2 corresponds to the case where the motors both rotate in the same direction, for example in forward gear, while part b corresponds to the case where the motors both operate in reverse gear. Of course, this does not exclude the possibility of turning one of the motors in forward gear while the other operates in reverse.

To rotate the first motor by one step forward, when the rotor occupies a determined rest position, it is sufficient to first send simultaneously in both coils B ₁₁ and B ₁₂ of the currents I ₁₁ to 1 ₁₂ positive and then inverting, when the rotor has turned about 90 °, the direction of the current 1 ₁₂ which becomes negative, without charging the direction of the current I ₁₁ .

To make the motor take a new step in the same direction, it is necessary to send first in the two coils B ₁₁ , B ₁₂ negative currents then, when the rotor has turned about half a step, reverse the direction of the current 1 ₁₂ in the second coil B ₁₂ .

Naturally, it is the same for the second engine. It is simply necessary to ensure that currents I ₂₁ and 1 ₂₂ are sent respectively to the first, B ₂₁ , and to the second coil 8 ₂₂ of this second motor, only when the coils of the first motor are not supplied. Note that, on the other hand, the coils of the first motor may very well be short-circuited during the sending of driving pulses to the second motor and vice versa.

To rotate the motors in reverse, starting from the same rest position as previously for the rotors, it is necessary to start by sending in their two coils currents I ₁₁ , 1 ₁₂ , respectively 1 ₂₁ , 1 ₂₂ , negative, then when the rotors have turned half a step, reverse the direction of the current in the first coils.

A new step will be taken in the same direction when the second coils receive positive currents and the second coils first positive, then negative currents.

In FIG. 2, the driving pulses applied to the two motors have been represented as having the same frequency and the same duration. It is clear that this will not always be the case. For example, in the known watch which has already been mentioned above where a first motor drives a second hand and a minute hand while a second motor advances an hour hand and a date indicator, in operating mode normal, the first motor will receive driving impulses every second and the second only every five minutes if the hour hand is driven at twelve steps per hour. In addition, the duration of the pulses will be longer for the second motor than for the first, since this second motor will have to drive a calendar mechanism.

FIG. 3 schematically represents an example of a control circuit which can be used in a watch, with the drive circuits of FIG. 1, to control two motors similar to that of the aforementioned German patent application.

In this example, the control signals of the transistors T ₁₁ to T ₁₆ and T ₂₁ to T ₂₆ (see FIG. 1) are supplied by a memory 4, of ROM type, which has six outputs, Si to S ₆ , which are directly connected to the gates of the transistors T ₁₁ to T ₁₆ of the first driver C, and six other outputs, S ₇ to S ₁₂ , which are also directly connected to the gates of the transistors T ₂₁ , to T ₂₆ of the second driver C ₂ . This memory also includes four address inputs, E, to E4, intended to receive logic signals, each combination of which corresponds to a blocking, short-circuiting or positive or negative current flow state in the different coils. B ₁₁ , B ₁₂ , B ₂₁ , and B ₂₂ .

The control circuit also includes an oscillator 1 including a quartz resonator and its maintenance circuit, a frequency divider 2 and a control logic 3 which develops, from signals of different frequencies delivered by the divider and from produced signals. by control means not shown, the logic signals which must be applied to the inputs of the read-only memory 4.

Oscillator 1 and divider 2 are conventional. As for the control logic, it will not be described in detail since its diagram depends on the function which is assigned to each of the motors and the automatic or manual means which are provided for controlling them.

The table below summarizes the operation of the circuit in the simple case where, firstly, the two coils of each motor are short-circuited for a determined time after the application of driving pulses to this motor and where secondly, the coils of one of the motors is supplied and then short-circuited only when the coils of the other motor are out of service, that is to say neither supplied with current nor short-circuited.

In this table, the four columns together called "STATES" indicate the different possible combinations of states of the four coils B ₁₁ , B ₁₂ , B ₂₁ and B ₂₂ . In these columns "OFF" means that the coil designated at the head is out of service, "CC" means that the coil is in short circuit, "+" and "-" that a positive current, respectively negative, crosses the coil.

The four columns entitled "INPUTS" give an example of the combinations of four logic signals which are applied to the inputs E ₁ to E4 of the memory 4.

Finally the twelve columns entitled "OUTPUTS" indicate the logical states that take the outputs Si to S, ₂ of the read-only memory for each of the combinations of the logical states of entry.

It is clear that this table is given for illustration only and that there are many other possibilities for controlling the two motors.

For example, as already indicated, one could short-circuit only one coil per motor instead of two, which would amount to modifying the 6th and 11th lines of the table. These same lines should be deleted if there was no question of shorting the coils after the driving pulses.

Furthermore, it may be advantageous to run the two motors almost at the same time, that is to say to apply driving impulses to the coils of one of the motors while the coils of the other motor are still short. -circuit.

It is also possible to short-circuit the coils of each motor for the entire period between two successive driving pulses. As in the previous case, for each driving circuit C ₁ , C ₂ , the short-circuiting of a coil must then be done sometimes by the P type transistors, sometimes by the N type transistors to whose drains this coil is connected, in the direction of the current in the other coil, when the latter is not itself short-circuited. For the various possibilities which have just been considered as well as for a certain number of others the number of combinations of states for the coils does not exceed sixteen and a memory with four inputs is sufficient. However, it may happen that we have to provide at least one additional entrance. For example, it is possible to control the motors by not suddenly reversing the current in one of the coils but by interrupting it first for a certain time. If, while remaining in the simple case where the coils of one of the motors are supplied while the coils of the other are put out of service after being short-circuited, this possibility is also used, we must add to the table below - above eight more beings for the coils and for the outputs of the memory. "OFF", "OFF", "+", "OFF" is an example of these additional states that must be provided for the coils.

Naturally, the invention is not limited to the particular mode of implementation which has just been described.

For example, it is possible to replace the MOS transistors of the two drive circuits with bipolar transistors.

Claims (1)

1. A control device for two bidirectional step motors of an electronic timepiece, each motor having a first and second coil, characterized by the fact that it includes:

   -two supply terminals (b_i, b₂) between which an electric energy source (P) can be connected;

   - a first driving circuit (C₁) which includes three circuit branches that are parallel connected between said supply terminals, each circuit branch-including two series-connected transistors (T₁₁― T₁₆) which can be controlled to apply current pulses of controlled polarity to the first coils (B₁₁, B₂₁) of the step motors, said first coils being, on the one hand, both connected to the junction of the transistors of one of the branches and, on the other hand, respectively connected to the junctions of the transistors of the two other branches;

   - a second driving circuit (C2) which also includes three branches that are parallel connected between said supply terminals, each circuit branch including two series-connected transistors (T₂₁―T₂₆) that can be controlled to apply current pulses of controlled polarity to the second coils (B₁₂, B₂₂) of the step motors, said second coils being, on the one hand, both connected to the junction of the transistors of one of the branches of that second circuit and, on the other hand, respectively connected to the junctions of the transistors of the two other branches; and

   - control means (1-4) for individually supplying control signals to each of said transistors of said first and second driving circuits so that the two coils of a motor simultaneously receive needed current pulses to make this motor turn and so as to prevent the simultaneous application of current pulses to a coil of one of the motors and to a coil of the other.

Images