EP0087387B1 - Method and means for controlling a bidirectional step-motor - Google Patents

Abstract

The invention concerns a method for controlling a bidirectional stepping motor having two windings and three pole faces. The invention comprises applying current pulses alternately to only one of the motor windings to cause it to rotate in one direction and to only the other of the motor windings to cause it to rotate in the other direction. The invention is used for controlling bidirectional motors which are employed in particular in timepieces.

Description

The present invention relates to a method and a device for controlling a bidirectional stepping motor comprising a stator comprising a frame which has a first, a second and a third pole face delimiting between them a substantially cylindrical space and which comprises a first and a second magnetic circuit respectively connecting the first pole face to the second pole face and the first pole face to the third pole face, the stator further comprising a first and a second coil magnetically coupled to the first, respectively to the second circuit magnetic, and the motor further comprising a rotor comprising a permanent magnet rotatably mounted in said space.

A motor as defined above is described in German patent application No. DE-A-3 026 004. According to this patent application, it is controlled by current pulses which are sent simultaneously in the two coils each time the rotor must turn one step, i.e. 180 °. The polarity of the current flowing in one of the coils is reversed substantially in the middle of the driving pulse.

The consumption of a motor controlled in this way is quite significant, since a current flows simultaneously in the two coils. In addition, the fact that the polarity of the current in one of the coils changes in the middle of the driving pulse implies that the motor control circuit comprises eight transistors forming, in a conventional manner, two bridges of four connected transistors, each, to one of the coils. These eight transistors, which must pass a fairly intense current, occupy a large area on the silicon wafer in which are integrated all the elements of the electronic circuit used to develop the driving pulses.

Bidirectional stepper motors comprising two coils magnetically coupled to a rotor comprising a permanent magnet, as well as their control methods, are already known.

Thus, for example, patent application GB-A-1 451 359 describes a motor having a stator which has four pole faces surrounding a rotor. This rotor comprises a magnet having two pairs of poles distributed regularly at its periphery. Two of the four pole faces are magnetically coupled to a first coil, and the other two pole faces are magnetically coupled to a second coil.

Still for example, patent application WO-A-81/02207 describes a motor whose rotor is a disc magnetized axially so as to present on each of its faces a plurality of magnetic poles alternately north and south. Two coils are coupled to this rotor by independent magnetic circuits, each having an air gap through which the periphery of the disc forming the rotor passes.

In the two above documents, the motor control method consists, for the two directions of rotation of the rotor, of applying pulses alternately to one and the other of the coils, two successive pulses on the same coil having opposite polarities from each other and the rotor rotating one step in response to each pulse. In patent application GB-A-1 451 359, the direction of rotation of the rotor from each of its stop positions depends on the polarity of the pulse applied to the coil which must be excited when the rotor is at this position. In application WO-A-81/02207, the direction of rotation of the rotor depends on the coil to which the pulse is applied.

Since the motors described in these two documents are very different from that described in patent application DE-A-3 026 004, their control methods are not applicable to the latter.

The purpose of the present invention is to provide a method and a device for controlling an engine such as that described in this patent application DE-A-3 026 004 which on the one hand make it possible to reduce the current consumption of the motor and, on the other hand, to use only six power transistors in the control circuit.

• -les figures 1 et 2 représentent une forme d'exécution du moteur;
• - la figure 3 est un tableau illustrant le procédé selon l'invention;
• - les figures 4a et 4b représentent des diagrammes des impulsions de commande du moteur;
• - la figure 5 est le schéma d'un exemple de circuit pour la mise en oeuvre du procédé;
• - les figures 6a et 6b sont des diagrammes représentant des signaux mesurés en divers points du schéma de la figure 5 pendant une rotation du moteur en marche avant, respectivement en marche arrière;
• - la figure 7 est un tableau illustrant une première variante du procédé selon l'invention;
• - la figure 8 est le schéma d'un exemple de circuit pour la mise en oeuvre de cette première variante du procédé;
• - les figure 9a et 9b sont des diagrammes représentant des signaux mesurés en divers points du circuit de la figure 8 pendant une rotation du moteur en marche avant, respectivement en marche arrière;
• - la figure 10 est un tableau illustrant une deuxième variante du procédé selon l'invention;
• - la figure 11 est le schéma d'un exemple de circuit pour la mise en oeuvre de cette deuxième variante;
• - les figures 12a et 12b sont des diagrammes représentant des signaux mesurés en divers points du circuit de la figure 11 pendant une rotation du moteur en marche avant, respectivement en marche arrière;
• - la figure 13 est un tableau illustrant une troisième variante du procédé selon l'invention;
• - la figure 14 est le schéma d'un exemple de circuit pour la mise en oeuvre de cette troisième variante;

This object is achieved by the method and by the device claimed in claims 1 and 7 which will be described with the aid of the drawing in which:

• FIGS. 1 and 2 represent an embodiment of the engine;
• - Figure 3 is a table illustrating the method according to the invention;
• - Figures 4a and 4b show diagrams of the motor control pulses;
• - Figure 5 is the diagram of an exemplary circuit for implementing the method;
• - Figures 6a and 6b are diagrams representing signals measured at various points in the diagram of Figure 5 during a rotation of the engine in forward, respectively in reverse;
• - Figure 7 is a table illustrating a first variant of the method according to the invention;
• - Figure 8 is the diagram of an example of a circuit for the implementation of this first variant of the method;
• - Figures 9a and 9b are diagrams representing signals measured at various points in the circuit of Figure 8 during a rotation of the engine in forward, respectively in reverse;
• - Figure 10 is a table illustrating a second variant of the method according to the invention;
• - Figure 11 is the diagram of an example of a circuit for the implementation of this second variant;
• - Figures 12a and 12b are diagrams representing signals measured in various points of the circuit of FIG. 11 during a rotation of the engine in forward, respectively in reverse;
• - Figure 13 is a table illustrating a third variant of the method according to the invention;
• - Figure 14 is the diagram of an example of a circuit for the implementation of this third variant;

• - la figure 16 est le schéma d'une variante du circuit de la figure 14; et
• - la figure 17 est le schéma d'une exemple de circuit permettant d'asservir la durée des impulsions motrices à la charge mécanique entraînée par le moteur.

FIGS. 15a and 15b are diagrams representing signals measured at various points in the circuit of FIG. 14 during a rotation of the motor in forward gear, in reverse respectively;

• - Figure 16 is the diagram of a variant of the circuit of Figure 14; and
• - Figure 17 is the diagram of an exemplary circuit for controlling the duration of the driving pulses to the mechanical load driven by the motor.

Figures 1 and 2 show an embodiment of the engine described in German patent application No. DE-OS 3.026.004 cited above. In this embodiment, the motor comprises a stator, the armature of which is formed of two pieces of soft magnetic material, one of which, designated by 1, has three branches designated by la, Ib and Ic, respectively, and whose l the other, designated by 2, has substantially the shape of a straight bar having three transverse projections, two of which, designated by 2a and 2b, are located at its ends, and the third of which, designated by 2c, is located in the middle. These two parts 1 and 2 of the stator armature are arranged relative to each other in the position shown in the drawing, in which they face each other, the arms 1a, 1b and 1c of part 1 being applied against the projections 2a, 2b and 2c, respectively, of the part 2 of the stator. The assembly is ensured by two screws 3, one of which crosses the branch 1a to be screwed into the projection 2a and the other of which crosses the branch 1b to be screwed into the projection 2b.

A circular hole 4 is formed in the part 1, in line with the birth of the branch 1c, median, of the latter, thus providing three thinned parts 1d, 1e and 1f, in the form of isthmus, connecting to each other the three pole faces formed one by the branch 1 c and the other two by the portions of the body of the part 1 even located between the thinning 1 d and 1e, and 1e and 1f respectively.

The motor rotor comprises a shaft 5 which pivots for example between two elements 6 and 7 of the frame of the apparatus which is equipped with the present motor. The shaft 5 carries a permanent magnet 8, bipolar, whose poles, diametrically opposite, have been indicated by N and S in FIG. 1.

The stator of the motor comprises two coaxial coils 9 and 10 wound on the two straight parts 2d of part 2 of the frame located one between the projection 2a and the projection 2c of part 2 and the other between the projection 2b and the projection 2c thereof. The magnetic field generated by each of these coils in space 4 and in magnet 8 when they are traversed by a current has been schematically represented in FIG. 1 where it is designated by C9, respectively C10.

It should be noted that, in the absence of current in the coils 9 and 10, the rotor is subjected to a positioning torque which tends to keep it in one or the other of two rest positions. One of these positions is that shown in FIG. 1, the other is that which the rotor occupies after having turned 180 °. The variation in this positioning torque as a function of the angle of rotation of the rotor is such that the rotor returns to the position it occupied if it is left free after being moved, in one direction or the other, by an angle less than approximately 90 °, and that it rotates to the other rest position if it is left free after being moved by an angle greater than approximately 90 °.

In FIG. 1, the directions of the fields C9 and C10 form angles of approximately 45 ° with the direction of the magnetization axis N - S of the magnet 8. In practice, these angles can be between 30 ° and 60 ° approximately, depending on the shape given to the different parts of the stator.

In the following of this description, the currents flowing in the coils 9 and 10 in a direction such that the magnetic field has the direction indicated by the arrows C9 and C10 will be arbitrarily qualified as positive. Likewise, the direction of rotation indicated by arrow 11 will be arbitrarily called positive direction of rotation.

The table in FIG. 3 illustrates the method according to the invention for controlling this motor. The signs + or - in the columns designated by 19 and 110 indicate that a positive, respectively negative current is sent to the coil 9, respectively 10, in the case illustrated by the line where they are located. The arrows in the columns designated by C9 and C10 indicate the direction of the field created by these currents. The arrows in the last three columns designated by Ra, Rb and Rc respectively indicate the starting position of the rotor, the position it would reach under the influence of the field created by the coils 9 or 10 if the current were maintained in these coils , and the position it reaches under the influence of the positioning torque when this current is interrupted. These various positions are indicated by arrows going from the south pole of magnet 8 to its north pole.

direction opposée à celle qu'il avait avant que le courant soit appliqué à la bobine 10 (colonne Rc).Line A in the table in Figure 3 illustrates how to control the motor so that the rotor turns one step, i.e. 180 °, in the positive direction from the position it occupies in FIG. 1. This position is recalled in the column Ra of this line A. A positive current pulse is sent to the coil 10. The field which results from this pulse has substantially the direction and the direction of the arrow C10 of the figure 1. No current is sent to the coil 9. The rotor is subjected to a torque such that, if the intensity of the current is sufficient, it turns in the positive direction until it reaches a position where the direction of the magnet 8 field is parallel to the direction of the arrow C10 (column Rb). If the current in the coil 10 is interrupted when the rotor reaches this position, it finishes its pitch under the influence of the positioning torque. It is then in the position where the field of the magnet

direction opposite to that which it had before the current was applied to the coil 10 (column Rc).

Line B of the table in FIG. 3 illustrates the way of controlling the motor so that the rotor turns again one step in the positive direction from the position it has reached following this first step. This position is symbolized in the column Ra of this line 8. A current pulse of the same intensity as that of line A of the table is sent to the coil 10, but in the negative direction. The resulting magnetic field therefore has the same direction as that of arrow C10, but the opposite direction. The torque exerted on the rotor therefore has the same direction as in the previous case, and the rotor turns again in the positive direction until the field of the magnet 8 has a direction parallel to that of the field. created by the current flowing in the coil 10 (column Rb). Again, when this current is interrupted, the rotor ends its pitch under the influence of the positioning torque. It is found in the position it occupies in Figure 1, after having made a full turn in the positive direction (column Rc).

It is obvious that if a positive current pulse is then again sent to the coil 10, the rotor repeats a step, as in the case of line A in the table of FIG. 3.

Line C of this table illustrates how to control the motor so that its rotor turns one step in the negative direction from the position it occupies in Figure 1 (column Ra).

In this case, a positive current pulse is sent to the coil 9, and no current is sent to the coil 10. The field which results from this pulse has substantially the direction and the direction of the arrow C9. The rotor is subjected to a torque such that it rotates in the negative direction until the direction of the field of the magnet 8 becomes parallel to the direction of the arrow C9 (column Rb). When this current is interrupted, the rotor ends its pitch under the influence of the positioning torque (column Rc). He therefore turned half a turn in the negative direction.

If a negative current pulse is now sent to the coil 9 (line D table in Figure 3), the resulting field has the same direction as arrow C9, but the opposite direction. The rotor therefore rotates, always in the negative direction, until the field of the magnet 8 has a direction parallel to that of this field created by the negative current in the coil 9 (column Rb). Again, when this current is interrupted, the rotor ends its pitch under the influence of the positioning torque (column Rc).

The rotor then made a full turn in the negative direction. If a positive current is again sent to the coil 9, the rotor repeats a step as in the case of line C.

It is clear that, in practice, the current must be interrupted at the latest when the rotor reaches the position illustrated by the column Rb of the table in FIG. 3, or even before. The duration of the current pulses sent into the coil 10 or into the coil 9 is chosen as a function of the characteristics of the motor and / or of the load which it drives.

It is easy to see that the direction of rotation of the rotor can be freely chosen, whatever its position. When the rotor is in the position it occupies in FIG. 1, a positive current pulse applied to the coil 10 causes a rotation in the positive direction, and a positive current pulse applied to the coil 9 causes a rotation in the negative sense. When the rotor is in the opposite position to that of FIG. 1, a negative current pulse applied to the coil 10 causes a rotation in the positive direction, and a negative current pulse applied to the coil 9 causes a rotation in the direction negative.

In summary, first current pulses are applied alternately in one direction and in the other only to one of the coils to cause the rotor to rotate in one direction, and second current pulses are applied alternately in one direction and in the other only to the other coil to cause the rotor to rotate in the other direction.

Figure 4a illustrates the current pulses sent to the coil 10 to rotate the rotor in the positive direction, and Figure 4b illustrates the pulses sent to the coil 9 to rotate the rotor in the negative direction.

In order for the rotor to turn half a step in response to one of these pulses, it must be in the desired position, that is, it must be in the position it occupies in FIG. 1, at the moment when a positive current pulse is sent to the coil 9 or to the coil 10 and that it must be in its other rest position at the time when a negative current pulse is sent to the either of these coils.

If, for any reason, this condition is not fulfilled, that is to say that the rotor is in the position of FIG. 1 and that a negative pulse is sent to one of the coils, or that it is in its other rest position and that a positive pulse is sent to this coil, the rotor begins to rotate in the opposite direction to that which corresponds to the coil in which the current is sent. However, it only turns at a small angle, less than the angle corresponding to half a step. The positioning torque to which it is subjected therefore does not change sign and the rotor returns to its starting position at the end of the pulse.

The next pulse will therefore have the correct polarity to rotate it one step in the desired direction. The direction of rotation is therefore not inverted when the rotor does not have the position it should have when a pulse is sent to one of the coils.

FIG. 5 shows the diagram of an example of a circuit for implementing the method according to the invention, and FIGS. 6a and 6b illustrate some signals measured at various points of this circuit.

In this example, as well as in the examples which will be described later, the motor is used in an electronic watch to drive the hands for displaying the hour, minute and second, not shown, using of a gear train also not shown. It is obvious that these examples are not limiting and that the invention can be used whatever the device or the apparatus in which the motor is incorporated.

The coils 9 and 10 of the motor are connected in a double bridge formed by six MOS transistors designated by T1 to T6. Transistors T1, T3 and T5 are p-type and have their source connected to the positive pole of the power source. The transistors T2, T4 and T6 are of type n and have their source connected to the negative pole of the power source. The drains of the transistors T1 and T2, T3 and T4, T5 and T6 are respectively connected to a first terminal of the coil 10, to the second terminal of the coil 10 and to a first terminal of the coil 9, and to the second terminal coil 9.

The gates G1 to G6 of the transistors T1 to T6 are connected to a logic circuit formed by six AND gates 21 to 26, two OR gates 27 and 28, four inverters 29 to 32 and two D-type flip-flops 33 and 34, connected to each other in the manner shown. This logic circuit will not be described in more detail here, since its operation, which is illustrated by the diagrams in FIGS. 6a and 6b, is easy to understand.

This logic circuit receives two periodic signals having respective frequencies of 1 Hz and 64 Hz supplied by outputs 35a and 35b of a frequency divider 35. This divider 35 receives from a quartz oscillator 36 a signal having a frequency of , for example, 32768 Hz. It also delivers on outputs designated 35c, 35d and 35e other periodic signals having frequencies of 128, 256 and 2048 Hz respectively which will be used in circuits described below.

The logic circuit also receives a signal AR for determining the direction of rotation of the motor, which is supplied, for example, by a time-setting circuit 38 which can be any one and which will not be described here.

In this example, this signal AR is in the logic state "0" when the rotor must turn in the positive direction, and in the logic state "1" when the rotor must turn in the negative direction.

It is easy to see that the output Q of the flip-flop 33 delivers control pulses which are in the state "1" for approximately 7.8 milliseconds, with a period of one second. Between these control pulses, the gates of transistors T1, T3 and T5 are in logic state "1" and the gates of transistors T2, T4 and T6 are in logic state "0". As these states "1" and "0" are represented respectively by the voltage of the positive terminal and by the voltage of the negative terminal of the power source, the six transistors T1 to T6 are blocked.

At the end of each control pulse delivered by the output Q of the flip-flop 33, the flip-flop 34 changes state. Its output Q therefore remains alternately in state "0" and in state "1" for one second.

It will be admitted at the outset that the output Q of the flip-flop 34 is in the state "0" and that its output Q is therefore in the state "1".

If the motor has to turn in the positive direction, the AR signal is at "0" (figure 6a). Under these conditions, a control pulse delivered by the output Q of the flip-flop 33 passes the gate 21 and reaches the gate G1 of the transistor T1 through the gate 23 and the inverter 30, and the gate G4 of the transistor T4 through gate 28. During the duration of this pulse, the gate G4 therefore passes to "1" and the gate G1 passes to "0". The transistors T1 and T4 therefore become conductive, and a current pulse crosses the coil 10 in the direction indicated by the arrow 36a. If the direction of the winding of the wire forming the coil 10 is chosen correctly, this pulse creates a magnetic field in the direction of arrow C10 in FIG. 1. This case therefore corresponds to the case of line A in the table in FIG. 3. If, in addition, the rotor is, before the start of the pulse, in the position shown in FIG. 1, it turns half a turn in the positive direction.

The end of the control pulse delivered by the Q output of the flip-flop 33 causes the flip-flop 34 to switch, the Q output of which goes to state "1". A second later, the output Q of the flip-flop 33 delivers a new control pulse which also passes through the gate 21 and this time reaches the gate G2 of the transistor T2 through the gate 24, and the gate G3 of the transistor T3 through the door 27 and the inverter 31. These two transistors therefore become conductive, and a current pulse crosses the coil 10 in the opposite direction to that of the arrow 36a. The rotor therefore turns again one step in the positive direction. This case corresponds to that of line B in the table in Figure 3.

This process is repeated at each control pulse delivered by the output Q of the flip-flop 33, as long as the signal AR remains at "0".

If this signal AR is in the state "1" (FIG. 6b), the control pulses delivered by the output Q of the flip-flop 33 pass through the gate 22. When the output Q of the flip-flop 34 is at "0 ", these pulses pass through gate 26 and reach gate G4 of transistor T4 through gate 28, and gate G5 of transistor T5 through inverter 32. These two transistors therefore become conductive, and a current pulse passes in coil 9 in the direction of arrow 37. This pulse creates a magnetic field in the direction of arrow C9 in FIG. 1, and the rotor turns one step in the negative direction. This case corresponds to that of line C in the table in Figure 3.

The following comma ·.:: G pulse, delivered one second later by output Q of flip-flop 33, also passes through gate 22. As output Q of flip-flop 34 is now in the state " 1 ", this pulse passes through gate 25 and reaches gate G6 of transistor T6. This pulse also reaches the gate G3 of the transistor T3 through the gate 27 and the inverter 31. These transistors T3 and T6 therefore become conductive and a current pulse crosses the coil 9 in the opposite direction to that of arrow 37. This case corresponds to that of the fourth line of the table in FIG. 3, and the rotor therefore turns again one step in the negative direction.

In summary, the device applies, in response to a control signal, a first current pulse to a first coil, alternately in one direction and in the other, when the signal for determining the direction of rotation of the rotor is in its first state, and a second current pulse to the second coil, alternately in one direction and in the other, when the signal for determining the direction of rotation of the rotor is in its second state. In the example described, the control signal consists of the pulses supplied by the output Q of the flip-flop 33.

The torque provided by the motor when controlled by the method described above is sufficient in most cases. It is however possible to increase this torque, if necessary, by using a variant of this method.

The table in FIG. 7 summarizes this first variant of the method according to the invention.

To turn the rotor one step in the positive direction, from the position it occupies in Figure 1, a positive current pulse is first applied to the coil 10, as in the method described above (see line A1 of the table in Figure 7). No current is sent to the coil 9. The field C10 created by this current brings the rotor to the position indicated in column Rb1 of this line A1.

The current in the coil 10 is then interrupted, and a current pulse of equally positive direction is applied to the coil 9 (line A2 of the table in FIG. 7). Field C9 resulting from this current brings the rotor to the position indicated in column Rb2.

When the current in the coil 9 is interrupted, the positioning torque brings the rotor to the position indicated in column Rc of line A2 of the table in FIG. 7.

To turn the rotor a second step, still in the positive direction, a negative current pulse is applied to the coil 10, then a negative current pulse is sent to the coil 9. Lines B1 and B2 of the table in FIG. 7 indicate these different currents, the resulting fields and the positions reached by the rotor in response to these fields and under the influence of the positioning torque.

To turn the rotor one step in the negative direction, from the position shown in Figure 1, a current pulse of positive direction is sent to the coil 9. A current pulse of also positive direction is then sent in the coil 10 and, finally, the positioning torque brings the rotor into its second rest position. The lines C1 and C2 in the table in FIG. 7 indicate these different currents, the resulting fields and the positions reached by the rotor in response to these fields and under the influence of the positioning torque.

To rotate the rotor in a new step in the negative direction, a current pulse of negative direction is sent to the coil 9, then a current pulse of negative direction is sent to the coil 10. Lines D1 and D2 of the table in Figure 7 indicate these different currents, the resulting fields and the positions reached by the rotor in response to these fields.

Thus, in this variant, as in the method described above, first current pulses are applied to a first coil alternately in a first direction and in the second direction to cause the rotation of the rotor in a first direction, and of the second Current pulses are applied to the second coil alternately in the first and in the second direction to cause the rotor to rotate in the second direction.

In addition, a third pulse is applied to the second coil after each first pulse, and a fourth pulse is applied to the first coil after each second pulse. The direction of the third or fourth pulse is the same as that of the first or, respectively, of the second immediately preceding pulse.

In this way, the torque supplied by the engine is notably increased, without its consumption increasing in the same proportions. In addition, it is always possible to control the motor using a circuit comprising only six power transistors.

FIG. 8 shows the diagram of an example of a circuit intended to implement this variant of the method according to the invention and FIGS. 9a and 9b are diagrams representing signals measured at a few points of this circuit.

The circuit of this figure 8 comprises a type D flip-flop 41, the output Q of which changes to "1" each time that the output 35a of the frequency divider 35, not shown in this figure, changes to the state "1 ". The reset input R of this flip-flop 41 is connected to the output 35c of the frequency divider 35, not shown, which supplies a signal at a frequency of 128 Hz. This output Q of the flip-flop 41 therefore returns to "0" 3.9 milliseconds after going to "1".

At this instant, the output Q of a second flip- type D 42 flop goes to state "1". The reset input R of this flip-flop 42 being connected to the output 35c of the divider 35 which supplies the signal at 128 Hz, through an inverter 43, its output Q also returns to the state "0" 3 , 9 milliseconds after going to "1".

A third type D flip-flop 44 switches at the end of each pulse supplied by the output Q of the flip-flop 42. The output Q of this flip-flop 44 therefore remains alternately at state "0" and at state "1" for one second.

The two consecutive control pulses supplied each second by the outputs Q of the two flip-flops 41 and 42 are transmitted to the gates G1 to G6 of the transistors T1 to T6, identical to those of FIG. 5 and not shown in this FIG. 8, by a logic circuit comprising AND gates 45 to 52, OR gates 53 to 56 and inverters 57 to 60, connected to each other as shown. This logic circuit will not be described in more detail here, since its operation, which is illustrated by the diagrams in FIGS. 9a and 9b, is easy to understand.

When the signal AR, which is identical to the signal AR of FIG. 5, is in the state "0" (FIG. 9a), and the output Q of the flip-flop 44 is also in the state "0", each first control pulse supplied by the output Q of the flip-flop 41 makes the transistors T1 and T4 conductive. A current pulse therefore passes in the positive direction in the coil 10 (line A1, FIG. 7). Under the same conditions, each second control pulse supplied by the output Q of the flip-flop 42 makes the transistors T4 and T5 conductive, which causes the passage of a current pulse in the coil 9, also in the positive direction ( line A2, figure 7).

When the signal AR is in the state "0" and the output Q of the flip-flop 44 is in the state "1", each first control pulse supplied by the output Q of the flip-flop 41 returns the transistors T2 and T3 conductors. A current pulse therefore passes through the coil 10 in the negative direction (line B1, FIG. 7). Each second control pulse supplied by the output Q of the flip-flop 42 makes the transistors T3 and T6 conductive. A current pulse therefore passes through the coil 9 also in the negative direction (line B2, FIG. 7).

When the signal AR is in state "1" (FIG. 9b) and the output a of the flip-flop 44 is in the state "0", each first control pulse supplied by the output Q of the flip-flop 41 causes the passage of a positive current pulse in the coil 9 (line C1, FIG. 7), and each second control pulse supplied by the output 9 of the flip-flop 42 causes the passage of an equally positive current pulse in coil 10 (line C2, Figure 7).

When the signal AR is in state "1", and the output Q of flip-flop 44 is also in state "1", each first control pulse supplied by output Q of flip-flop 41 causes the passage of a negative current pulse in the coil 9 (line D1, figure 7), and each second control pulse supplied by the output 9 of the flip-flop 42 causes the passage of a current pulse, also negative, in coil 10 (line D2, Figure 7).

In summary, the device of FIG. 8 delivers to the coils of the motor, in response to a control signal, the same first and second pulses as the device of FIG. 5. In addition, it applies a third current pulse to the second coil after each first pulse and a fourth current pulse to the first coil after each second pulse. The third and the fourth pulse is _t the same direction as the first, respectively the second immediately preceding pulse.

In this example, the control signal consists of the pulses supplied by the outputs Q of the flip-flops 41 and 42.

In the example of this FIG. 8, the control pulses delivered by the outputs Q of the flip-flops 41 and 42 follow each other without interval and they have durations equal, each one, to half of the duration of the pulses supplied by the output Q of the flip-flop 33 in the case of FIG. 5. This is not however compulsory, and it is possible to choose for these control pulses different durations, to adapt them to the characteristics of the motor and / or of the load. that it entails. It is also possible to leave a small gap between them.

The table in FIG. 10 summarizes a second variant of the method according to the invention.

To rotate the rotor one step in the positive direction, from the position it occupies in Figure 1, a current pulse of negative direction is first applied to the coil 9 (line A1 of the table in Figure 10). No current is sent to the coil 10. The field C9 created by this pulse brings the rotor to the position indicated in column Rb1 of this line A1.

The current in the coil 9 is interrupted, and a current pulse of positive direction is applied to the coil 10 (line A2 in the table of FIG. 10). No current is sent to the coil 9. The field C10 resulting from this pulse brings the rotor to the position indicated in column Rb2. When the current in the coil 10 is interrupted, the positioning torque brings the rotor to the position indicated in column Rc of line A2.

To turn the rotor a second step, still in the positive direction, a current pulse of positive direction is applied to the coil 9, then a current pulse of negative direction is sent to the coil 10. Lines 81 and 82 of the table of FIG. 10 indicate these different currents, the resulting fields and the positions reached by the rotor in response to these fields and under the influence of the positioning torque.

To rotate the rotor one step in the direction negative, from the position indicated in figure 1, a current pulse of negative direction is sent in the coil 10. A current pulse of positive direction is then sent in the coil E'3t, finally, the positioning torque brings the rotor to its second rest position. Lines C1 and C2 in the table in Figure 10 indicate these different currents, the resulting fields and the positions reached by the rotor in response to these fields and under the influence of the positioning torque.

To rotate the rotor in a new direction in the negative direction, a positive current pulse is sent to the coil 10, then a negative current current pulse is sent to the coil 9. Lines D1 and D2 of the The table in FIG. 10 indicates these different currents, the fields which result therefrom and the positions reached by the rotor in response to these fields and to the positioning torque.

Thus, in this second variant, as in the method and in the first variant described above, first current pulses are applied to a first coil, alternately in a first direction and in the second direction to cause the rotation of the rotor in a first direction, and second current pulses are applied to the second coil, alternately in the first and in the second direction to cause the rotor to rotate in the second direction. As in the first variant, a third pulse is applied to the second coil after each first pulse, and a fourth pulse is applied to the first coil after each second pulse.

It should be noted, however, that in this second variant, the coil to which the first pulses are applied is that to which the second pulses are applied in the process and in the first variant, and vice versa. Likewise, the direction of the current which must be applied to cause the rotation of the rotor in a determined direction from a determined position is each time the inverse of the direction of the current which is applied under the same conditions in the process and in its first variant. In addition, contrary to what happens in the first variant, the direction of this third and of this fourth pulse is each time the opposite direction of the direction of the first or, respectively, of the second immediately preceding pulse.

FIG. 11 illustrates an example of a circuit allowing the implementation of this variant of the method, and FIGS. 12a and 12b are diagrams representing signals measured at some points of this circuit when the rotor turns respectively in the positive direction and in the negative sense.

The flip-flops 41, 42 and 44 and the reverser 43 represented in FIG. 11 are exactly the same and operate in the same way as those in FIG. 8.

The two control pulses supplied by the outputs of the flip-flops 41 and 42 are transmitted to the gates G1 to G6 of the transistors T1 to T6, identical to those of FIG. 5 and not shown in this FIG. 11, by a logic circuit comprising the AND gates 71 to 82, OR gates 83 to 88, and inverters 89 to 92, connected to each other as shown.

This circuit will not be described in more detail, because it is easy to see, with the aid of FIGS. 12a and 12b, that the first control pulses supplied by the output Q of flip-flop 41 cause the passage of the first pulses of current in the coil 9 or the passage of the second current pulses in the coil 10 depending on the state of the signal AR, and that the second control pulses supplied by the output Q of the flip-flop 42 cause the passage of the third current pulses in coil 10 or fourth current pulses in coil 9, always according to the state of the AR signal. The direction of these current pulses is further determined by the state of the outputs Q and Q of the flip-flop 44. This state changes at the end of each pulse supplied by the output Q of the flip-flop 42, that is to say i.e. at the end of each rotor step.

The control of the motor according to a third variant of the method makes it possible to increase the torque supplied by this motor, compared to that which it provides when it is controlled according to the second variant, without increasing its consumption to a great extent.

The table in Figure 13 summarizes this third variant. The lines A1, A2, B1, B2, C1, C2, D1 and D2 in this table are identical to the corresponding lines in the table in Figure 10.

To turn the rotor one step in the positive direction, from the position it occupies in FIG. 1, a current pulse of negative direction is applied to the coil 9, then a current pulse of positive direction is applied to the coil 10, as in the second variant described above (lines A1 and A2 in Figure 13).

Then, a current pulse is sent again in the coil 9, in the positive direction this time, without the current being interrupted in the coil 10. The fields C9 and C10 which result from these currents combine to exert on the rotor a torque which is added to the positioning torque to bring the rotor to its second rest position (line A3 in Figure 13).

To turn the rotor in a new step in the positive direction, a positive current pulse is sent to the coil 9, then a negative direction pulse is sent to the coil 10 (lines B1 and B2 of Figure 13).

Then, a negative direction pulse is sent again into the coil 9, without the current being interrupted in the coil 10. The fields C9 and C10 which result from these currents combine again to exert a torque which is added to the positioning torque for return the rotor to the position it occupies in Figure 1 (line B3 in Figure 13).

Similarly, to rotate the rotor in a negative direction from the position it occupies in Figure 1, the same current pulses as in the second variant are applied to the coils 9 and 10 (lines C1 and C2 in Figure 13), then a positive current pulse is sent to the coil 10 without the current being interrupted in the coil 9 (line C3 in Figure 13).

To turn the rotor in a new step in the negative direction, the same current pulses as in the second variant are applied to the coils 9 and 10 (lines D1 and D2 in Figure 13) then a negative current pulse is sent to the coil 10 without the current being interrupted in the coil 9 (line D3 in FIG. 13).

In summary, in this third variant, the first, second, third and fourth current pulses are applied as in the second variant. In addition, a fifth current pulse is applied to the first coil after the start of each third pulse and a sixth current pulse is applied to the second coil after the start of each fourth pulse, without this third or fourth pulse being interrupted. The direction of the fifth or sixth current pulse is the opposite direction to the direction of the immediately preceding first or second pulse.

FIG. 14 illustrates an example of a circuit allowing the implementation of this third variant of the method, and FIG. 15 is a diagram representing signals measured at a few points of this circuit.

The circuit of FIG. 14 comprises a D-type flip-flop 101 whose clock input Ck receives the signal having a frequency of 1 Hz from the output 35a of the divider 35, not shown in this figure (see fig. 5). The output Q of this flip-flop 101 is connected to its input D, so that its output Q goes to state "1" each time the signal having a frequency of 1 Hz itself goes to state "1". The reset input R of the flip-flop 101 receives from the output 35d of the divider 35 a signal having a frequency of 256 Hz. The output Q of the flip-flop 101 therefore returns to the state "0" approximately 1, 9 milliseconds after entering state "1". At this instant, the output Q of a flip-flop 102, also of type D, the input Ck of which is connected to the output Õ of the flip-flop 101, changes to state "1". As the reset input R of this flip-flop 102 receives, through an inverter 103, the signal having a frequency of 256 Hz supplied by the output 35d of the divider 35, the output Q of this flip-flop 102 returns in state "0" about 1.9 milliseconds after going to state "1". At this instant, the output Q of a flip-flop 104 also of type D, the input Ck of which is connected to the output Q of the flip-flop 102, changes to state "1". The input R of this flip-flop 104 also receiving the signal having a frequency of 256 Hz, its output Q returns to the state "0" also about 1.9 milliseconds after having passed to the state "1".

The outputs Q of the flip-flops 101, 102 and 104 therefore deliver each second three successive pulses.

Each time the output Õ of the flip-flop 104 goes to state "1", a flip-flop 105, also of type D, flips. Its output Q therefore remains alternately in state "0" and in state "1" for one second.

The three control pulses supplied respectively by the outputs Q of the flip-flops 101, 102 and 104 are transmitted to the gates G1 to G6 of the transistors T1 to T6, identical to those of FIG. 5 and not represented in this FIG. 14, by a logic circuit comprising AND gates 106 to 117, OR gates 118 to 125 and inverters 126 to 129, connected to each other as shown.

This logic circuit will not be described in more detail, because it is easy to see, with the aid of FIGS. 15a and 15b, that, as in the second variant described above, the first control pulses supplied by the output 9 of the flip-flop 101 cause the passage of the first current pulses in the coil 9 or the passage of the second current pulses in the coil 10 depending on the logic state of the signal AR, and that the second control pulses supplied by the output Q flip-flop 102 cause the passage of the third current pulses in the coil 10 or the fourth current pulses in the coil 9, always according to the state of the signal AR. In addition, the third control pulses supplied by the output Q of the flip-flop 104 maintain the third or the fourth current pulses, and at the same time cause the passage of the fifth current pulses in the coil 9, in the opposite direction of that of the first immediately preceding pulse, or the passage of the sixth current pulses in the coil 10, in the opposite direction to that of the immediately preceding second pulse.

These three control pulses supplied by the outputs Q of the flip-flops 101, 102 and 104 have equal durations in the example described above. It is obvious that these pulses could have different durations, adapted to the characteristics of the motor and / or of the load which it drives.

In the third variant of the method described above, a current flows in the two coils of the motor during the fifth or sixth pulses. The power source of the device must therefore supply, during these fifth or sixth pulses, twice as much current as during the other pulses. This can lead to a momentary decrease in the voltage of this source, with all the drawbacks which are linked to such a decrease.

To avoid these drawbacks, it is possible to interrupt the current alternately in one and in the other of the coils during the fifth, respectively the sixth pulses. In this way, the power source of the device must supply the same current in all cases.

The circuit of FIG. 16, which is a complement to the circuit of FIG. 14, makes it possible to carry out this interruption of the current alternately in one and in the other coil during these fifths, respectively sixth pulses. This circuit comprises four AND gates 131 to 134 each having a first input connected, respectively, to the output of one of the gates 120 to 123 of FIG. 14. The outputs of these gates 131 to 134 are connected respectively to the input of the inverter 127, at the gate G2, at the input of the inverter 129, and at the gate G6.

An AND gate 135 has its first input connected to the output Q of the flip-flop 104 of FIG. 14, and its second input connected to the output 35e of the divider 35 of FIG. 5, not shown in this FIG. 16. This output delivers a signal having a frequency of, for example, 2048 Hz. The output of gate 135 is connected, through an inverter 136, to the second inputs of gates 131 and 132. Another AND gate 137 has its first input also connected to the output Q of the flip-flop 104 and its second input connected, by the intermediary of an inverter 138, to the output 35e of the divider 35. The output of the door 137 is connected, by means of an inverter 139, at the second inputs of doors 133 and 134. The rest of the circuit of FIG. 14 is not modified.

When, during a third command pulse supplied by the output Q of the flip-flop 104, the two coils must be traversed by positive currents (case of lines A3 and C3 in the table of FIG. 13), the outputs of the gates OR 120 and 122 go to state "1". FIG. 16 shows that, in this case, the gate G5 of the transistor T5 is only put in the state "0" when the signal at 2048 Hz is in the state "1". Likewise, the gate G1 of the transistor T1 is only set to the "0" state when this signal at 2048 Hz is in the "0" state. The transistor T1 is therefore blocked when the transistor T5 is conductive, vice versa. The transistor T4, on the other hand, remains permanently conductive. It follows that the two coils are traversed alternately by the current.

When the two coils must be traversed by negative currents (case of lines B3 and D3 in the table of figure 13), it is the outputs of the OR gates 121 and 123 which pass to the state "1". In this case, the gate G6 of the transistor T6 is only set to the state "1" when the signal at 2048 Hz is also in the state "1", and the gate G2 of the transistor T2 is not set to state "1" when this signal is in state 220 ". The transistor T2 is therefore blocked when the transistor T6 is conductive, and vice versa.

The transistor T3, on the other hand, remains conductive at all times. As a result, the two coils are also traversed alternately by a current.

In the method and its variants described above, the durations of the various pulses are predetermined. It is of course possible to adjust the duration of these pulses to the magnitude of the load actually driven by the motor, to reduce as much as possible the electrical energy consumption of the system.

The circuits making this adjustment, which are well known and which will not be described here, generally measure the value of an electrical quantity dependent on the current flowing in the coil, compare this measured value with a reference value and use the result of this comparison to control the duration of the driving pulses to the load driven by the motor.

These circuits generally include a resistor connected in series with the motor coil. The voltage drop across this resistor, which is proportional to the current flowing in the coil, is used as the input variable to the servo circuit. The presence of this resistance causes a reduction in the voltage applied to the motor and an increase in the consumption of the system.

In the method according to the invention and in its first two variants, only one of the two coils is traversed at each instant by a current. It is the same, in the third variant, during the first and the second control pulse.

This feature allows the duration of the first, second, third and fourth pulses of current to be enslaved to the load driven by the motor without having to connect a resistor in series with the coils. It suffices for this, for example, to measure during each current pulse applied to one of the coils the voltage induced in the other coil, which is not traversed by the current. This measurement can be used to adjust the duration of the current pulses.

FIG. 17 illustrates an example of a circuit implementing this servo-control method, applied to the case of FIG. 5.

All the elements described in this figure 5, with the exception of the frequency divider 35 and the oscillator 36, are reproduced in this figure 17, with the same references.

The circuit of FIG. 17 includes a measurement circuit 141 which can be of any type and which will not be described in detail here. The circuit of FIG. 17 further comprises six transmission doors 142 to 147 and an OR gate 148. The output of this gate 148 is connected to the reset input R of the flip-flop 33. One of the inputs of the door 148 is connected to the output 35b of the divider 35, not shown, and the other of its inputs is connected to the output of the circuit 141. The first terminals of the transmission doors 142 and 143 are connected, together, to the drain transistors T1 and T2, and therefore at one of the terminals of the coil 10. The first terminals of the transmission gates 144 and 145 are connected, together, to the drain of the transistors T3 and T4, that is to say to the other terminal of the coil 10 and to one of the terminals of the coil 9. The first terminals of the transmission doors 146 and 147 are connected, together, to the drain of the transistors T5 and T6, that is to say to the other terminal of the coil 9. The second terminals of the doors 142, 144 and 146 are connected, together, to one of the inputs of the measurement circuit 141 and the second terminals of the doors 143, 145 and 147 are connected together to the other input of this measurement circuit 141.

The control electrodes of the transmission doors 142 to 147 are connected, respectively, to the outputs of doors 26, 25, 27, 28, 23 and 24. In this way, when a positive current flows through the coil 10, the doors of transmission 145 and 146 are conductive, and the measurement circuit 141 is connected to the terminals of the coil 9. When a negative current flows through this coil 10, the transmission gates 144 and 147 are conductive, and the measurement circuit 141 is also connected to the terminals of the coil 9, but in the opposite direction to the previous direction. The polarity of the signal applied to the inputs of circuit 141 is therefore the same in both cases.

When a positive current passes through the coil 9, the transmission doors 142 and 145 are conductive, and it is the coil 10 which is connected to the inputs of the circuit 141. When a negative current passes through the coil 9, the doors transmission 143 and 144 are conductive and the coil 10 is also connected to the inputs of the circuit 141, in the opposite direction to the previous one. The polarity of the signal applied to these inputs is therefore the same in these two cases.

Whatever the coil through which a current flows, the output of circuit 114 delivers a signal "1" when, for example, the voltage applied to its inputs exceeds a determined value. This signal resets the output Q of the flip-flop 33 to "0", which interrupts the current flowing in the coil used.

If, for one reason or another, the output of circuit 141 does not go to state "1", the output Q of flip-flop 33 is nevertheless reset to state "0" by the signal from the output 35b of the divider 35, as in the case of FIG. 5. This arrangement avoids that the flip-flop 33 does not remain indefinitely engaged, and therefore that current does not circulate permanently in one of the coils.

Other circuits could be provided, in particular a circuit in which the measurement of the voltage induced in the coil not traversed by the current would not be carried out during each pulse, but at longer intervals. This measurement would be used to determine a pulse duration which would then be memorized and which would be used for the following pulses.

The circuit 141 could also be produced in the form of a circuit detecting only the rotation or the non-rotation of the rotor. The current pulses would normally all have the same duration. When the circuit 141 detects that the rotor has not rotated in response to one of these normal pulses, a catch-up pulse, of greater duration than the normal duration, would then be sent to the motor by its control circuit.

It is obvious that the same kind of circuit could be adapted without difficulty to the case of FIGS. 8 and 11.

Claims (13)

1. Method for controlling a bidirectional stepping motor including a stator comprising a core (1, 2) which presents a first, a second and a third pole face defining therebetween a substantially cylindrical space (4) and which includes a first and a second magnetic circuit respectively coupling the first pole face to the second pole face and the first pole face to the third pole face, the stator moreover comprising a first (9) and a second (10) winding coupled respectively to the first and the second magnetic circuit and the motor further including a rotor comprising a permanent magnet (8) rotatably mounted in said space (4), characterized in that it consists in apply alternately in a first and in a second sense, in order to effect rotation of the rotor by one step in a first sense for each of the first pulses and in applying second current pulses solely to the second winding (10) alternately in the first sense and in the second sense, to effect rotation, of the rotor by one step in the second sense for each of the second pulses, no current being applied to the second winding (10) over the duration of the first pulses and no current being applied to the first winding (9) over the duration of the second pulses.

2. Method according to claim 1, characterized in that it consists in applying to the second winding (10), following each first pulse, a third current pulse having the same sense as the immediately preceding first pulse and in applying to the first winding (9), following each second pulse, a fourth current pulse having the same sense as the immediately preceding second pulse.

3. Method according to claim 1, characterized in that it consists in applying to the second winding (10) following each first pulse, a third current pulse the sense of which is inverted from that of the immediately preceding first pulse,and in applying to the first winding (9), following each second pulse, a fourth current pulse the sense of which is inverted from that of the immediately preceding second pulse.

4. Method according to claim 3, characterized in that it consists in applying to the first winding (9) after the beginning of each third pulse, a fifth pulse the sense of which is inverted from that of the immediately preceding first pulse, and in applying to the second winding (10), after the beginning of each fourth pulse, a sixth pulse. the sense of which is inverted from that of the immediately preceding second pulse.

5. Method according to claim 4, characterized in that it consists in measuring, at least during a pulse applied to one of the windings (9, 10), the voltage induced in the other winding (9, 10) and in adjusting the duration of said pulses in response to the value of said induced voltage.

6. Method according to any of claims 1, 2 or 3, characterized in that in consists in measuring, at least during a pulse applied to one of the windings (9, 10), the voltage induced in the other winding (9, 10), and in adjusting the duration of said pulses in response to the value of said induced voltage.

7. Control arrangement for a bidirectional stepping motor including a stator comprising a core which presents a first, a second and a third pole face defining therebetween a substantially cylindrical space (4) and which includes a first and a second magnetic circuit respectively coupling the first pole face to the second pole face and the first pole face to the third pole face, the stator moreover comprising a first (9) and a second (10) winding coupled respectively to the first and the second magnetic circuit, and the motor further including a rotor comprising a permanent magnet (8) rotatably mounted in said space (4), the control arrangement including means (38) for supplying a signal having a first and a second state to determine the rotation sense of the rotor (AR), and means (35, 35) for supplying a control signal each time the rotor is to turn through a step, characterized in that it includes furthermore control means (27 - 34; 41 - 60; 71 - 92; 101 - -129) for supplying, in response to the control signal, a first current pulse solely to the first winding (9), alternately in a first sense and in the second sense for effecting rotation of the rotor by one step in a first sense for each of said first pulses when the signal to determine the rotation sense (AR) is in its first state, and for supplying a second pulse solely to the second winding (10) alternately in the first and in the second sense, for effecting rotation of the rotor by one step in the second sense for each of the second pulses when the signal to determine the rotation sense is in its second state.

8. Control arrangement according to claim 7, characterized in that the control means (21 - 34; 41 - 60; 71 -92; 101 - 729) include means (42,46, 47, 53, 54) for supplying, in response to the control signal, a third current pulse to the second winding (10) following each first pulse and a fourth current pulse to the first winding (9) following each second pulse, the third and fourth current pulses having the same sense as the respective first and second immediately preceding pulses.

9. Control arrangement according to claim 7, characterized in that the control means (21 - 34; 41 - 60; 71 - 92; 101 - -129) include means (42, 72, 74, 76, 78, 80, 82, 83 - 86) for supplying, in response to the control signal, a third current pulse to the second winding (10) following each first pulse and a fourth current pulse to the first winding (9) following each second pulse, the third and fourth current pulses having the sense inverted from the sense of the respective first and second immediately preceding pulses.

10. Control arrangement according to claim 9, characterized in that the control means (21 - 34; 41 -60; 71 - 92; 101 - 129) include means (104, 111, 112, 115, 116, 118, 119, 120 - 123) for supplying in response to a control signal, a fifth current pulse to the first winding (9) after the beginning of each third pulse and a sixth currenfpulse to the second winding (10) after the beginning of each fourth pulse, the fifth and the sixth current pulses having the sense inverted from the sense of the respective first and second immediately preceding pulses.

11. Control arrangement according to claim 10, characterized in that it further includes means (131 - 139) for alternately interrupting the third and the fifth pulse over the duration of the fifth pulse and for alternately interrupting the fourth and the sixth pulse over the duration of the sixth pulse.

12. Control arrangement according to claim 7 characterized in that it further includes means (141) for measuring, at least during a pulse supplied to a winding (9, 10), the voltage induced in the other winding (9, 10), means (142 - 147) for selectively coupling the measuring means (141) to said other winding (9, 10) in response to the signal (AR) to determine the rotation sense and to the control signal, and means (148) for adjusting the duration of the pulses in response to the measured induced voltage.

13. Control arrangement according to either of claims 8 or 9, characterized in that it further includes means (141) for measuring, at least during a pulse supplied to a winding (9, 10), the voltage induced in the other winding (9, 10), means (142 - 147) for selectively coupling the measuring means (141) to said other winding (9, 10) in response to the signal (AR) to determine the rotation sense and to the control signal, and means (148) for adjusting the duration of the pulses in response to the measured induced voltage.

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