EP0062273B1 - Method of controlling a stepping motor - Google Patents

Method of controlling a stepping motor Download PDF

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Publication number
EP0062273B1
EP0062273B1 EP82102626A EP82102626A EP0062273B1 EP 0062273 B1 EP0062273 B1 EP 0062273B1 EP 82102626 A EP82102626 A EP 82102626A EP 82102626 A EP82102626 A EP 82102626A EP 0062273 B1 EP0062273 B1 EP 0062273B1
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Prior art keywords
duration
pulse
pulses
motor
control
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EP82102626A
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German (de)
French (fr)
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EP0062273A1 (en
Inventor
Mai Tu Xuan
Michel Grosjean
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Omega SA
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Omega SA
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    • G—PHYSICS
    • G04—HOROLOGY
    • G04C—ELECTROMECHANICAL CLOCKS OR WATCHES
    • G04C3/00—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means
    • G04C3/14—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means incorporating a stepping motor
    • G04C3/143—Means to reduce power consumption by reducing pulse width or amplitude and related problems, e.g. detection of unwanted or missing step

Definitions

  • the present invention relates to a method for controlling a single-phase stepping motor supplied by a train of bipolar pulses with the load presented by the mechanism of a timepiece. It offers various improvements to the servo system which has been described in patent application EP-A-0 022 270.
  • a supply device making it possible to detect the position of the rotor of a stepping motor with respect to the polarity of the driving pulses and to send to said motor a train of long pulses if this polarity is judged to be incorrect.
  • the rotor does not advance one step after having sent a motor pulse of correct polarity, it will receive a predetermined period of time later (a second for example) a new pulse of incorrect polarity and it is from this moment that the system comes into operation, the correction or the catch-up taking place by sending to the motor two long-lasting close pulses followed by a train of very large pulses.
  • the system proposed in the cited application envisages only two types of pulses: narrow pulses when the torque exerted on the motor is low and broad pulses when this torque has increased beyond a certain limit .
  • this couple can take very diverse values due, for example, to one of the following events or the combination of some of these events: change of calendar, friction in the bearings and their wear, aging oils, drop in temperature, influence of an external magnetic field, linear or angular shocks, manufacturing tolerances, etc.
  • Figure 1 of this presentation shows schematically a motor whose poles of the stator are separated by air gaps 1.
  • all the flux ⁇ ab from the magnetized rotor 2 passes through the core of the coil 3 to produce at the terminals of this coil a induced voltage Ui when the rotor is moving.
  • the air-gap motor receives a pulse of correct polarity, the voltage Ui collected across its coil will be of a sufficiently high amplitude to decide that it must continue to supply it with pulses of small width. It is a different matter if the system described in the cited application is applied to an engine with saturable zones.
  • Figure 2 schematically shows such a motor where the stator poles are joined by isthmus 4. In this case, we see that the flux created by the magnet is divided into a flux ⁇ f passing through the isthmus and into a flux ⁇ 1> ab passing through the core of the coil.
  • This method although applied to a motor with saturable isthmus, does not provide a system which maintains the saturation of the isthmus during the measurement of the induced voltage and this in order to obtain a signal of large amplitude, as is the case. case in the present invention. This method also does not indicate how it should go about detecting a comfortable amplitude voltage when the duration of the control pulse increases.
  • the pulses referenced n - 2 to n + 4 are the control pulses received by the motor coil. The start of each of them is separated by a constant period of time, for example one second, which advances the seconds hand of the watch in steps of one second.
  • This clock signal comes from the output of a chain of frequency dividers which is itself supplied by a time base oscillator according to an arrangement which is now well known.
  • two very large catch-up pulses T are sent to the motor to catch up with this delay at a short time after the end of the pulse n.
  • the first catch-up pulse is in the same direction as the n -1 pulse and the second in the opposite direction so that the large width pulses T a are somehow substituted to the control pulses n - 1 and n of width Tl which were not able to advance the rotor of the motor.
  • the duration T a is naturally chosen to be long enough to cause the rotor to progress under the most unfavorable load conditions.
  • the process which has just been described shows that the duration of the control pulses is adapted to the load imposed on the motor by successive rising levels when the load increases.
  • the process therefore makes it possible to save energy and this in even greater proportions than if only two types of pulses were available, as provided for in the cited application.
  • six different pulses have been chosen whose motor durations range from 3 to 9 ms in successive levels of 0.5 ms for the first three, 1.5 ms for the fourth and fifth and 2 ms for the sixth.
  • the duration of the catch-up pulse was chosen at 8 ms. This will appear in more detail when the diagram shown in Figure 12 is explained.
  • FIG. 4 presents a second variant of the method according to the invention where, after sending two catch-up pulses, the motor is still supplied with a pair of pulses of the same duration as that which existed before the correction.
  • the control pulses n + 1 and n + 2 have the same duration T, as that of the pulses n - 1 and n.
  • binding events have a fleeting nature such that they disappear very quickly.
  • An attempt to refuel the motor a second time with pulses whose duration did not advance its rotor a first time can be fruitful because, if the attempt succeeds, an increase in consumption will have been avoided due to an unnecessary widening of the pulses control. If the attempt is unsuccessful, the motor is supplied with pulses of longer duration T 2 after having sent the two catch-up pulses.
  • This second variant is not limited to the renewed sending of a single pair of pulses of the same duration TI and it will be understood that means can be used to continue supplying the motor with the pulses T, as long as a given number of catch-up pulses will not have been counted in a predetermined interval. For example, it can be decided that if the rotor has missed its step four times for 60 seconds, these missed steps having been followed by four pulses catch-up, then the motor is supplied with pulses of duration T2.
  • FIG. 5 shows the evolution of the positioning torque Ca and of the mutual torque Cab as found in a stepping motor.
  • the angular positions S ′ 2 , S, and S 2 are the stable equilibrium positions of the rotor and the positions l ′ 1 and I 1 are the unstable equilibrium positions of this rotor. Normally if the rotor takes its step in response to a positive impulse, it goes from position S, to position S 2 . In the particular case which has just been mentioned, it is therefore possible that the rotor stops in position 11 which represents only a half-step stroke. Although this position is unstable, it is possible that the rotor is maintained there by the frictions which act on it.
  • the rotor will either reverse into position SI, or advance into position S 2 .
  • the new control pulse will have an incorrect polarity and the catch-up pulses T a will make up for the two lost steps.
  • the rotor will have caught up with the lost step itself and no catching pulse will be sent to it.
  • the situation presents itself differently if the rotor remains fixed in position I 1 when the next pulse occurs. Indeed, this next negative impulse develops the mutual torque -Cab which happens to be in the same direction as the negative positioning torque -Ca.
  • FIG. 6 shows an arrangement which overcomes the drawback cited by proposing, according to a particular embodiment of the invention, to send to the motor coil a predetermined period of time after the end of the duration control pulse T t , a safety pulse of duration T S.
  • a pulse of very short duration will suffice to send it either to S 1 or to S 2 .
  • a negative safety pulse will bring it back to S, and the next normal command pulse will show up as incorrect, which will trigger the two catch-up pulses as explained above.
  • a positive safety pulse will bring the rotor to S 2 ; in this case, the next command pulse will appear to be correct and no catch-up will take place.
  • a negative safety pulse will be preferred since it takes less energy to bring the rotor from position 1 1 to position S, than from position I 1 to position S 2 .
  • a duration between 0.2 and 0.5 ms is chosen for T s and for the period of time separating the end of the control pulse from the safety pulse a duration of the order of 50 ms.
  • FIG. 7 shows the device used to obtain a very comfortable voltage Ui even if the motor is of the type with saturable zones.
  • This device comprises a bridge with four branches, each of which comprises a switch, the first diagonal of the bridge receiving a continuous power source and the second comprising the motor coil.
  • a resistor is arranged in series with this coil and is bridged by a switching device. Means are put into action to open said device when it is necessary to detect the rotation or the absence of rotation of the rotor.
  • FIG. 7 shows a resistor 40 connected in series with the coil 15 of the motor, a resistor which can be short-circuited when the switch 35 is closed.
  • the switch control sequence is established according to the table below for a positive pulse:
  • transistors play the role of switches. They receive their signals from a conventional shaping circuit.
  • U B is the only driving voltage useful to drive the rotor.
  • the resistor 40 is connected in series with the coil 15, the switch 35 is open. It is the period of measurement intended to take at the terminals of the coil the induced voltage Ui developed by the motor.
  • FIG. 9 represents the behavior of the motor during the measurement period T X.
  • the control voltage U is applied to the terminals 41 and 42 of the circuit which comprises the coil 3 and the resistor 40 connected in series.
  • the value of the resistance 40 is chosen so as to generate in the coil 3 a current l SAT which, in turn, will produce a flux ⁇ b sufficient to saturate the isthms 4 of the stator.
  • the flux ⁇ b produces across the coil an induced voltage where N b represents the number of turns of the coil.
  • FIG. 8 shows that at a predetermined time t x of the period T x , the voltage Ui, shown in dashed lines, is of large amplitude as a result of which the motor will continue to be supplied with the same width control pulses T n .
  • the induced voltage Ui will be measured in an interval T Ui included in the period T x , interval which can embrace, for example, the last two thirds of the period T X.
  • the shortest TRB period a duration of 3 ms and for the period T x a duration of 1 ms while the value of the resistance 40 is 15 kQ for a resistance of the coil. 3 kQ.
  • FIG. 10 illustrates the phenomenon which has just been explained and shows how the amplitude of the voltage Ui decreases when the pulse U B lengthens. It can be seen that the driving pulses of increasing duration U B1 , U B2 and U B3 correspond respectively to the induced voltages Ui 1 , Ui 2 and Ui 3 , the maximum of said voltages being located on an envelope whose shape is representative of the coupling factor. Cab / i, down to speed. For the U 84 pulse, the figure shows that no induced voltage is detected.
  • Figure 11 shows how we proceed according to a particular embodiment of the invention to overcome the drawback mentioned.
  • the control pulse U is composed of two driving pulses U B and U c separated by a period T x during which the induced voltage is measured according to the method which has been explained above.
  • the width T t of the control pulse U is greater than the duration T n from which the amplitude of the induced voltage Ui would be insufficient or zero, said induced voltage Ui is measured during an interval T Ui included in the period T x immediately preceding the end of the period T n .
  • the window method is also perfectly suitable if it is applied to a motor with air gaps (see Figure 1) where the phenomenon of extinction of the induced voltage also exists when the control pulse lengthens.
  • the coil of the motor with an open circuit can also be placed, as recommended in application EP-A-0 022 270, when it is desired to measure the induced voltage. If this is the case, the resistor 40 and the switch 35 shown in FIG. 7 will be deleted and all the switches 31 to 34 will be opened during the duration measurement window T X. It must also be said that if the open circuit voltage Ui is measured in the air gap motor, the graph in FIG. 11 remains the same except for the current i which is canceled out during the period T X.
  • FIG. 12 illustrates in an exemplary manner how the width of the control pulse is adapted to the load imposed on the motor and when the induced voltage is measured.
  • Figure 12 also shows the catch-up pulse of duration T, the width of which is chosen at 8 ms.
  • the voltage Ui is compared with a reference voltage in a comparator. If Ui is greater than said reference, a pulse of correct polarity has been sent to the motor and no signal appears at the output of the comparator. The control circuit continues to send pulses of the same duration. If, on the contrary, Ui is smaller than the reference, an incorrect polarity pulse has been sent to the motor and a signal appears at the output of the comparator which forces the control circuit to send two catching pulses then a control pulse train, as explained above.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Control Of Stepping Motors (AREA)
  • Electromechanical Clocks (AREA)

Description

La présente invention est relative à un procédé pour asservir un moteur pas à pas monophasé alimenté par un train d'impulsions bipolaires à la charge présentée par le mécanisme d'une pièce d'horlogerie. Elle propose diverses améliorations au système d'asservissement qui a été décrit dans la demande de brevet EP-A-0 022 270.The present invention relates to a method for controlling a single-phase stepping motor supplied by a train of bipolar pulses with the load presented by the mechanism of a timepiece. It offers various improvements to the servo system which has been described in patent application EP-A-0 022 270.

Dans la demande citée, il est exposé un dispositif d'alimentation permettant de détecter la position du rotor d'un moteur pas à pas par rapport à la polarité des impulsions motrices et d'envoyer audit moteur un train d'impulsions de longue durée si cette polaritè est jugée incorrecte. En d'autres termes, si le rotor ne progresse pas d'un pas après que lui ait été envoyée une impulsion motrice de polarité correcte, il recevra un laps de temps prédéterminé plus tard (une seconde par exemple) une nouvelle impulsion de polarité incorrecte et c'est à partir de ce moment-là que le système entre en fonction, la correction ou le rattrapage s'opérant en envoyant au moteur deux impulsions rapprochées de longue durée suivies d'un train d'impulsions de grande largeur.In the cited application, there is disclosed a supply device making it possible to detect the position of the rotor of a stepping motor with respect to the polarity of the driving pulses and to send to said motor a train of long pulses if this polarity is judged to be incorrect. In other words, if the rotor does not advance one step after having sent a motor pulse of correct polarity, it will receive a predetermined period of time later (a second for example) a new pulse of incorrect polarity and it is from this moment that the system comes into operation, the correction or the catch-up taking place by sending to the motor two long-lasting close pulses followed by a train of very large pulses.

On s'est rendu compte cependant que le détecteur exposé dans cette demande présente plusieurs inconvénients qui vont être passés en revue maintenant..We have realized, however, that the detector exposed in this application has several drawbacks which will be reviewed now.

D'abord, le système proposé dans la demande citée n'envisage que deux types d'impulsions: des impulsions étroites quand le couple exerce sur le moteur est faible et des impulsions larges quand ce couple a augmenté au-delà d'une certaine limite. Dans la pratique, on constate cependant que ce couple peut prendre des valeurs très diverses dues, par exemple, à l'un des évènements suivants ou la combinaison de certains de ces événements: changement du calendrier, frottement dans les paliers et leur usure, vieillissement des huiles, baisse de la température, influence d'un champ magnétique extérieur, chocs linéaires ou angulaires, tolérances de fabrication, etc.. Dans la demande citée, avec un choix limité à deux largeurs d'impulsions seulement, il faudra ou bien choisir un premier type d'impulsions à durée très faible avec le risque de voir l'asservissement fonctionner très souvent lorsque survient le moindre des événements cités ou bien choisir un premier type d'impulsions à durée plus grande pour ne faire intervenir l'asservissement qu'occasionnellement lorsque survient un couple important, celui du changement de calendrier par exemple. Quelle que soit la solution choisie, on comprendra que le système proposé, bien que consommant moins d'énergie qu'un système sans asservissement, n'est pas apte à réagir finement, c'est-à-dire à adapter la consommation de courant à la charge réelle qui se présente sur le moteur de la montre.First, the system proposed in the cited application envisages only two types of pulses: narrow pulses when the torque exerted on the motor is low and broad pulses when this torque has increased beyond a certain limit . In practice, however, it can be seen that this couple can take very diverse values due, for example, to one of the following events or the combination of some of these events: change of calendar, friction in the bearings and their wear, aging oils, drop in temperature, influence of an external magnetic field, linear or angular shocks, manufacturing tolerances, etc. In the cited request, with a choice limited to only two pulse widths, it will either be necessary to choose a first type of pulse of very short duration with the risk of seeing the servo function very often when the least of the events mentioned occurs, or else choose a first type of pulse of longer duration to only involve the servo occasionally when a significant couple occurs, that of the change of calendar for example. Whichever solution is chosen, it will be understood that the proposed system, although consuming less energy than a system without servo-control, is not capable of reacting finely, that is to say of adapting the current consumption to the actual load on the watch motor.

Ensuite, si le système de la demande citée est bien adapté à un moteur pas à pas dont les pôles du stator sont séparés par un entrefer, il l'est beaucoup moins à un moteur dit à zones saturables dont les pôles se rejoignent par des isthmes de faible largeur. La figure 1 du présent exposé montre schématiquement un moteur dont les pôles du stator sont séparés par des entrefers 1. Dans ce cas, tout le flux Φab issu du rotor aimanté 2 traverse le noyau de la bobine 3 pour produire aux bornes de cette bobine une tension induite Ui lorsque le rotor est en mouvement. Dans la demande EP-A-022 270, il est prévu de mesurer la tension induite Ui immédiatement après la fin de l'impulsion motrice, la bobine étant mise en circuit ouvert. Si le moteur à entrefers reçoit une impulsion de polarité correcte, la tension Ui recueillie aux bornes de sa bobine sera d'une amplitude suffisamment élevée pour décider qu'on doit continuer à l'alimenter avec des impulsions de faible largeur. Il en va autrement si l'on applique le système décrit dans la demande citée à un moteur à zones saturables. La figure 2 montre schématiquement un tel moteur où les pôles du stator sont réunis par des isthmes 4. Dans ce cas, on voit que le flux créé par l'aimant se partage en un flux Φf passant par les isthmes et en un flux <1>ab passant par le noyau de la bobine. Il ressort de ceci que si l'on applique le système de la demande citée (c'est-à-dire qu'on mesure la tension Ui aux bornes d'une bobine mise circuit ouvert) à un moteur à zones saturables, on recueillera une tension induite de faible amplitude, ce qui n'est évidemment pas favorable au bon fonctionnement de l'électronique de commande.Then, if the system of the cited request is well suited to a stepping motor whose poles of the stator are separated by an air gap, it is much less so to a motor known as with saturable zones whose poles are joined by isthmus narrow. Figure 1 of this presentation shows schematically a motor whose poles of the stator are separated by air gaps 1. In this case, all the flux Φab from the magnetized rotor 2 passes through the core of the coil 3 to produce at the terminals of this coil a induced voltage Ui when the rotor is moving. In application EP-A-022 270, provision is made to measure the induced voltage Ui immediately after the end of the driving pulse, the coil being placed in open circuit. If the air-gap motor receives a pulse of correct polarity, the voltage Ui collected across its coil will be of a sufficiently high amplitude to decide that it must continue to supply it with pulses of small width. It is a different matter if the system described in the cited application is applied to an engine with saturable zones. Figure 2 schematically shows such a motor where the stator poles are joined by isthmus 4. In this case, we see that the flux created by the magnet is divided into a flux Φ f passing through the isthmus and into a flux <1> ab passing through the core of the coil. It follows from this that if one applies the system of the quoted demand (that is to say that one measures the voltage Ui at the terminals of an open circuit coil) to a motor with saturable zones, one will collect a low amplitude induced voltage, which is obviously not favorable to the proper functioning of the control electronics.

Enfin, puisque la demande citée n'envisage une détection de tension induite qu'après les seules impulsions de faible largeur où on peut détecter une tension d'amplitude confortable, on ne sait rien du procédé qu'il faudrait mettre en oeuvre si l'on voulait détecter une tension encore suffisante produite après une impulsion de plus longue durée, tant il est vrai, comme cela apparaîtra par la suite, que la tension induite diminue rapidement lorsque l'impulsion de commande s'allonge.Finally, since the cited request envisages an induced voltage detection only after the only pulses of small width where it is possible to detect a voltage of comfortable amplitude, nothing is known of the process which should be implemented if the we wanted to detect a still sufficient voltage produced after a longer pulse, as it is true, as will appear later, that the induced voltage decreases rapidly when the control pulse is extended.

On a cité dans le rapport de recherche l'exposé no 3 (pages 67-72) présenté par M. Ueda et al. au 10e Congrès international de chronométrie tenu à Genève du 11 au 14 septembre 1979 et ayant le titre " Adaptive controlled drive system of stepping motor for analog quartz watch". Dans cet exposé est divulgué un procédé pour asservir un moteur pas à pas alimenté par un train d'impulsions bipolaires de commande dans le but de réduire au minimum la consommation d'énergie. Ledit procédé envisage d'augmenter progressivement, c'est-à-dire par niveaux, la durée des impulsions de commande si une tension détectée indique que le moteur n'a pas progressé d'un pas. Si, par contre, aucune absence de rotation du rotor n'est détectée pendant une période prédéterminée, on fait diminuer la durée des impulsions motrices d'un niveau et ainsi de suite.Reference no. 3 was cited in the research report (pages 67-72) presented by M. Ueda et al. at the 10th International Chronometry Congress held in Geneva from 11 to 14 September 1979 and having the title "Adaptive controlled drive system of stepping motor for analog quartz watch". In this talk there is disclosed a method for controlling a stepper motor powered by a train of bipolar control pulses in order to minimize energy consumption. Said method envisages gradually increasing, that is to say by levels, the duration of the control pulses if a detected voltage indicates that the motor has not progressed by one step. If, on the other hand, no absence of rotation of the rotor is detected for a predetermined period, the duration of the driving pulses is made to decrease by one level and so on.

Ce procédé, bien qu'appliqué à un moteur à isthmes saturables, ne propose pas un système qui maintient la saturation des isthmes pendant la mesure de la tension induite et ceci dans le but d'obtenir un signal de grande amplitude, comme cela est le cas dans la présente invention. Ce procédé n'indique pas non plus comment il faudrait s'y prendre pour détecter une tension d'amplitude confortable quand la durée de l'impulsion de commande s'allonge.This method, although applied to a motor with saturable isthmus, does not provide a system which maintains the saturation of the isthmus during the measurement of the induced voltage and this in order to obtain a signal of large amplitude, as is the case. case in the present invention. This method also does not indicate how it should go about detecting a comfortable amplitude voltage when the duration of the control pulse increases.

C'est le but de la présente invention de remédier aux inconvénients qui viennent d'être cités en proposant des procédés selon les revendications 1 et 2.It is the object of the present invention to remedy the drawbacks which have just been mentioned by proposing methods according to claims 1 and 2.

L'invention sera mieux comprise maintenant à la lumière de la description qui suit et pour l'intelligence de laquelle on se référera, à titre d'exemple, au dessin dans lequel:

  • La figure 1 est une représentation schématique d'un moteur connu dont les pôles du stator sont séparés par des entrefers.
  • La figure 2 est une représentation schématique d'un moteur connu dont les pôles du stator sont séparés par des isthmes.
  • La figure 3 est un diagramme représentant les diverses impulsions appliquées au moteur selon une première variante de l'invention.
  • La figure 4 est un diagramme représentant les diverses impulsions appliquées au moteur selon une seconde variante de l'invention. m
  • La figure 5 est un graphique représentant les couples mutuel et de positionnement du moteur en fonction de la position a de son rotor.
  • La figure 6 est un diagramme montrant comment est alimenté le moteur par des impulsions de sécurité selon l'invention.
  • La figure 7-montre le dispositif utilisé dans le procédé selon l'invention.
  • La figure 8 est un graphique qui représente les diverses tensions que l'on trouve aux bornes de la bobine du moteur de même que le courant qui la traverse.
  • La figure 9 est une représentation schématique d'un moteur. dont les pôles du stator sont séparés par des isthmes auquel est appliqué le dispositif selon la figure 7.
  • La figure 10 est un graphique qui montre comment évolue l'amplitude de la tension induite quand l'impulsion motrice s'allonge.
  • La figure 11 est un graphique qui montre comment on procède pour mesurer la tension induite quand l'impulsion de commande dépasse une durée déterminée.
  • La figure 12 est un diagramme illustrant les diverses durées d'impulsion qui se présentent dans l'alimentation du moteur selon l'invention.
The invention will be better understood now in the light of the following description and for the understanding of which one will refer, by way of example, to the drawing in which:
  • Figure 1 is a schematic representation of a known motor whose poles of the stator are separated by air gaps.
  • Figure 2 is a schematic representation of a known motor whose poles of the stator are separated by isthmus.
  • FIG. 3 is a diagram representing the various pulses applied to the motor according to a first variant of the invention.
  • FIG. 4 is a diagram representing the various pulses applied to the motor according to a second variant of the invention. m
  • FIG. 5 is a graph representing the mutual and positioning torques of the motor as a function of the position a of its rotor.
  • FIG. 6 is a diagram showing how the motor is supplied with safety pulses according to the invention.
  • Figure 7-shows the device used in the method according to the invention.
  • Figure 8 is a graph showing the various voltages found across the motor coil as well as the current flowing through it.
  • Figure 9 is a schematic representation of an engine. the poles of the stator of which are separated by isthmus to which the device according to FIG. 7 is applied.
  • FIG. 10 is a graph which shows how the amplitude of the induced voltage changes when the driving pulse lengthens.
  • FIG. 11 is a graph which shows how one proceeds to measure the induced voltage when the control pulse exceeds a determined duration.
  • FIG. 12 is a diagram illustrating the various pulse durations which occur in the supply of the motor according to the invention.

On se reportera d'abord au diagramme de la figure 3 pour comprendre comment on procède pour asservir le moteur pas à pas selon une première variante de l'invention. Les impulsions référencées n - 2 à n + 4 sont les impulsions de commande que reçoit la bobine du moteur. Le début de chacune d'elles est séparé par un laps de temps constant, par exemple une seconde, ce qui fait progresser l'aiguille des secondes de la montre par pas de une seconde. Ce signal d'horloge provient de la sortie d'une chaîne de diviseurs de fréquence alimentée elle- meme par un oscillateur formant base de temps selon une disposition désormais bien connue.We will first refer to the diagram in FIG. 3 to understand how we proceed to slave the stepping motor according to a first variant of the invention. The pulses referenced n - 2 to n + 4 are the control pulses received by the motor coil. The start of each of them is separated by a constant period of time, for example one second, which advances the seconds hand of the watch in steps of one second. This clock signal comes from the output of a chain of frequency dividers which is itself supplied by a time base oscillator according to an arrangement which is now well known.

Dans les conditions de marche optimum, c'est-à-dire lorsque les événements contraignants dont il a été parlé plus haut ne se présentent pas, le moteur travaille pratiquement à vide et une impulsion de très faible largeur TI, telle celle représentée en n - 2 sur le diagramme, suffit à faire avancer normalement l'aiguille des secondes. On va supposer maintenant qu'après l'impulsion n - 2, à laquelle le moteur a encore répondu, le couple mécanique augmente subitement dû au concours conjugué de plusieurs événements contraignants. Le rotor ne réagira donc pas à l'impulsion n - 1 et, lors de l'arrivée de la prochaine impulsion n, il ne réagira pas non plus puisque pour le faire progresser il lui faudrait recevoir à ce moment-là une impulsion de signe négatif. Ainsi, le rotor a perdu deux pas qu'il s'agit de rattraper. Selon l'idée déjà exprimée dans la demande EP-A-0 022 270, on envoie au moteur pour rattraper ce retard deux impulsions de rattrapage de grande largeur Ta un court laps de temps après la fin de l'impulsion n. Comme on le voit sur la figure 3, la première impulsion de rattrapage se présente dans le même sens que l'impulsion n -1 et la seconde dans le sens opposé de telle sorte que les impulsions de grande largeur Ta se substituent en quelque sorte aux impulsions de commande n - 1 et n de largeur Tl qui n'ont pas été à même de faire progresser le rotor du moteur. La durée Ta est choisie naturellement assez longue pour provoquer à coup sùr la progression du rotor dans les conditions de charge les plus défavorables. Le graphique de la figure 3 exagère cependant cette durée Ta par rapport à la durée Tl dans le but de bien faire ressortir le fonctionnement du système. L'invention présente l'originalité, par rapport à l'invention revendiquée dans la demande déjà citée, de ne pas poursuivre avec un train d'impulsions fixes de grande largeur sitôt après les impulsions de rattrapage, mais d'allonger quelque peu l'impulsion de commande de durée TI en durée T2 et d'essayer si cette nouvelle impulsion pourrait être de durée suffisamment longue pour faire tourner le rotor. Si tel n'est pas le cas, on fait suivre les nouvelles impulsions n + 1 et n + 2 de durée T2 par deux nouvelles impulsions de rattrapage de durée Ta comme cela est illustré en figure 3. A leur tour, les impulsions de rattrapage sont suivies par de nouvelles impulsions de commande n + 3, n + 4 de durée T3 légèrement supérieure à la durée T2. Si elles sont capables de mettre le moteur en rotation, on poursuit avec les impulsions de durée T3, sinon on envoie les impulsions de rattrapage pour procédér ensuite avec des impulsions de largeur T4 ou T3 < T4 et ainsi de suite.In optimum operating conditions, that is to say when the constraining events of which we have spoken above do not occur, the engine works practically at no load and a very narrow width pulse TI, such as that represented in n - 2 on the diagram, suffices to advance the seconds hand normally. We will now assume that after the impulse n - 2, to which the motor has responded again, the mechanical torque suddenly increases due to the combined effect of several constraining events. The rotor will therefore not react to impulse n - 1 and, when the next impulse n arrives, it will not react either since to make it progress it would have to receive at that time a sign impulse negative. Thus, the rotor has lost two steps that need to be caught. According to the idea already expressed in the application EP-A-0 022 270, two very large catch-up pulses T are sent to the motor to catch up with this delay at a short time after the end of the pulse n. As seen in Figure 3, the first catch-up pulse is in the same direction as the n -1 pulse and the second in the opposite direction so that the large width pulses T a are somehow substituted to the control pulses n - 1 and n of width Tl which were not able to advance the rotor of the motor. The duration T a is naturally chosen to be long enough to cause the rotor to progress under the most unfavorable load conditions. The graph in FIG. 3 however exaggerates this duration T a with respect to the duration T l in order to clearly show the operation of the system. The invention has the originality, compared to the invention claimed in the aforementioned application, of not continuing with a train of fixed pulses of large width immediately after the catch-up pulses, but of somewhat lengthening the TI duration control pulse in T2 duration and to try if this new pulse could be of sufficiently long duration to turn the rotor. If this is not the case, the new pulses n + 1 and n + 2 of duration T 2 are followed by two new catch-up pulses of duration T a as illustrated in FIG. 3. In turn, the pulses catch-up are followed by new control pulses n + 3, n + 4 of duration T3 slightly greater than the duration T2. If they are able to put the motor in rotation, we continue with the pulses of duration T 3 , otherwise we send the catch-up pulses to then proceed with pulses of width T 4 or T3 <T4 and so on.

Ainsi, le procédé qui vient d'être décrit montre qu'on adapte la durée des impulsions de commande à la charge imposée au moteur par niveaux successifs montants lorsque la charge augmente. Le procédé permet donc d'économiser de l'énergie et ceci dans des proportions encore plus importantes que si l'on n'avait à disposition que deux types d'impulsions seulement, comme cela était prévu dans la demande citée. Dans une réalisation particulière, on a choisi six impulsions différentes dont les durées motrices s'étendent de 3 à 9 ms par niveaux successifs montants de 0,5 ms pour les trois premières, de 1,5 ms pour les quatrième et cinquième et de 2 ms pour la sixième. Dans cette même réalisation, la durée de l'impulsion de rattrapage-a été choisie à 8 ms. Ceci apparaîtra plus en détail lorsqu'on expliquera le diagramme représenté en figure 12.Thus, the process which has just been described shows that the duration of the control pulses is adapted to the load imposed on the motor by successive rising levels when the load increases. The process therefore makes it possible to save energy and this in even greater proportions than if only two types of pulses were available, as provided for in the cited application. In a particular embodiment, six different pulses have been chosen whose motor durations range from 3 to 9 ms in successive levels of 0.5 ms for the first three, 1.5 ms for the fourth and fifth and 2 ms for the sixth. In this same embodiment, the duration of the catch-up pulse was chosen at 8 ms. This will appear in more detail when the diagram shown in Figure 12 is explained.

On va supposer maintenant que, pour des impulsions n + 3, n + 4, etc., de durée T3, le moteur progresse normalement sans détection d'absence de pas. On peut penser qu'au bout d'une période prédéterminée les évènements contraignants qui avaient fait passer la durée des impulsions de TI à T3 ont cessé. On va donc faire descendre la durée des impulsions de commande de T3 à T2. Si le résultat est satisfaisant pendant une même période prédéterminée, on pourra encore baisser d'un niveau et passer de la durée T2 à la durée TI. Ladite période prédéterminée sera choisie à la suite d'observations qui auront été conduites sur la marche de la pièce d'horlogerie en fonction des diverses circonstances qui peuvent se présenter. Elle a été choisie dans la réalisation particulière dont il a été question plus haut à 512 secondes. En résumé, on adapte la durée des impulsions de commande à la charge imposée au moteur par niveaux successifs descendants lorsque la charge diminue.We will now assume that, for pulses n + 3, n + 4, etc., of duration T 3 , the motor progresses normally without detecting the absence of steps. One can think that at the end of a predetermined period the constraining events which had made pass the duration of the impulses of TI to T3 stopped. So we will do lower the duration of the control pulses from T3 to T2. If the result is satisfactory during the same predetermined period, it will be possible to further decrease by one level and go from the duration T 2 to the duration TI. Said predetermined period will be chosen following observations which will have been carried out on the running of the timepiece according to the various circumstances which may arise. It was chosen in the particular realization which was mentioned above at 512 seconds. In summary, the duration of the control pulses is adapted to the load imposed on the motor by successive descending levels when the load decreases.

La figure 4 présente une seconde variante du procédé selon l'invention où, après l'envoi de deux impulsions de rattrapage, on alimente encore le moteur par une paire d'impulsions de même durée que celle qui existait avant la correction. Dans la figure, les impulsions de commande n + 1 et n + 2 ont la même durée T, que celle des impulsions n - 1 et n. On peut penser en effet qu'en certaines circonstances les évènements contraignants ont un caractère fugitif tel qu'ils disparaissent très rapidement. Une tentative de réalimenter le moteur une seconde fois par des impulsions dont la durée n'a pas fait progresser son rotor une première fois peut être fructueuse car, si la tentative aboutit, on aura évité une augmentation de consommation due à un élargissement inutile des impulsions de commande. Si la tentative n'aboutit pas, on alimente le moteur avec des impulsions de durée plus longue T2 après lui avoir envoyé les deux impulsions de rattrapage.FIG. 4 presents a second variant of the method according to the invention where, after sending two catch-up pulses, the motor is still supplied with a pair of pulses of the same duration as that which existed before the correction. In the figure, the control pulses n + 1 and n + 2 have the same duration T, as that of the pulses n - 1 and n. One might think, in fact, that in certain circumstances, binding events have a fleeting nature such that they disappear very quickly. An attempt to refuel the motor a second time with pulses whose duration did not advance its rotor a first time can be fruitful because, if the attempt succeeds, an increase in consumption will have been avoided due to an unnecessary widening of the pulses control. If the attempt is unsuccessful, the motor is supplied with pulses of longer duration T 2 after having sent the two catch-up pulses.

Cette seconde variante n'est pas limitée à l'envoi renouvelé d'une seule paire d'impulsions de même durée TI et on comprendra que des moyens peuvent être mis en oeuvre pour continuer à alimenter le moteur avec les impulsions T, tant qu'un nombre donné d'impulsions de rattrapage n'aura pas été compté dans un intervalle prédéterminé.Ainsi, par exemple, on peut décider que si le rotor a manqué quatre fois son pas pendant 60 secondes, ces pas manqués ayant été suivis par quatre impulsions de rattrapage, on alimente alors le moteur par des impulsions de durée T2.This second variant is not limited to the renewed sending of a single pair of pulses of the same duration TI and it will be understood that means can be used to continue supplying the motor with the pulses T, as long as a given number of catch-up pulses will not have been counted in a predetermined interval. For example, it can be decided that if the rotor has missed its step four times for 60 seconds, these missed steps having been followed by four pulses catch-up, then the motor is supplied with pulses of duration T2.

Puisque dans le procédé décrit, on fait en sorte que la durée des impulsions de commande soit juste suffisante pour entraîner le mécanisme, on s'est rendu compte que dans certains cas, assez rares il est vrai, le rotor, après avoir démarré normalement à la suite d'une impulsion de polarité correcte, s'arrête après avoir parcouru un demi-pas seulement.Since in the process described, we make sure that the duration of the control pulses is just sufficient to drive the mechanism, we have realized that in some cases, quite rare it is true, the rotor, after starting normally at following a pulse of correct polarity, stops after having traveled only half a step.

La figure 5 montre l'évolution du couple de positionnement Ca et du couple mutuel Cab tels qu'on les trouve dans un moteur pas à pas. Les positions angulaires S'2, S, et S2 sont les positions d'équilibre stable du rotor et les positions l'1 et I1 sont les positions d'equilibre instable de ce rotor. Normalement si le rotor franchit son pas en réponse à une impulsion positive, il passe de la position S, à la position S2. Dans le cas particulier qui vient d'être évoqué, il se peut donc que le rotor s'arrête en position 11 qui ne représente qu'une course d'un demi-pas. Bien que cette position soit instable, il est possible que le rotor s'y maintienne par les frottements qui agissent sur lui. Si avant que ne survienne la prochaine impulsion de commande une perturbation quelconque est appliquée à la montre, le rotor soit reculera en position SI, soit avancera en position S2. Dans le premier cas, la nouvelle impulsion de commande présentera une polarité incorrecte et les impulsions de rattrapage Ta feront rattraper les deux pas perdus. Dans le second cas, le rotor aura rattrappé lui-même le pas perdu et aucune impulsion de rattrapage ne lui sera envoyée. La situation se présente différemment si le rotor reste fixé sur la position I1 quand survient la prochaine impulsion. En effet, cette prochaine impulsion négative développe le couple mutuel -Cab qui se trouve être dans le même sens que le couple négatif de positionnement -Ca. Si le couple -Cab est très élevé, il est possible alors que, conjugué au couple -Ca, il développe assez d'énergie pour déplacer le rotor de la position 11 à la position S'2 sans s'arrêter à la position S1, ce déplacement s'opérant sans qu'il y ait eu détection de polaritê incorrecte. Le rotor se fixe de façon stable en position S'2. A partir de ce moment-là, la prochaine impulsion, dirigée dans le sens positif, développera le couple mutuel Cab dessiné en traits interrompus et le rotor progressera normalement. On tire de ce raisonnement que le rotor a perdu définitivement deux pas qu'il ne sera pas possible de rattraper.FIG. 5 shows the evolution of the positioning torque Ca and of the mutual torque Cab as found in a stepping motor. The angular positions S ′ 2 , S, and S 2 are the stable equilibrium positions of the rotor and the positions l ′ 1 and I 1 are the unstable equilibrium positions of this rotor. Normally if the rotor takes its step in response to a positive impulse, it goes from position S, to position S 2 . In the particular case which has just been mentioned, it is therefore possible that the rotor stops in position 11 which represents only a half-step stroke. Although this position is unstable, it is possible that the rotor is maintained there by the frictions which act on it. If before the next command pulse occurs any disturbance is applied to the watch, the rotor will either reverse into position SI, or advance into position S 2 . In the first case, the new control pulse will have an incorrect polarity and the catch-up pulses T a will make up for the two lost steps. In the second case, the rotor will have caught up with the lost step itself and no catching pulse will be sent to it. The situation presents itself differently if the rotor remains fixed in position I 1 when the next pulse occurs. Indeed, this next negative impulse develops the mutual torque -Cab which happens to be in the same direction as the negative positioning torque -Ca. If the torque -Cab is very high, it is possible then that, combined with the torque -Ca, it develops enough energy to move the rotor from position 1 1 to position S ' 2 without stopping at position S 1 , this displacement taking place without there having been an incorrect polarity detection. The rotor is fixed stably in position S ' 2 . From this moment, the next pulse, directed in the positive direction, will develop the mutual torque Cab drawn in broken lines and the rotor will progress normally. We draw from this reasoning that the rotor has definitely lost two steps that it will not be possible to catch up with.

La figure 6 montre un arrangement qui palie l'inconvénient cité en proposant selon un mode particulier de réalisation de l'invention d'envoyer à la bobine du moteur un laps de temps prédéterminé après la fin de l'impulsion de commande de durée Tt, une impulsion de sécurité de durée TS. Si l'on se reporte de nouveau à la figure 5, on comprendra que, si le rotor est bloqué en position 11, il suffira d'une impulsion de durée très courte pour le faire parvenir soit en S1 soit en S2. Une impulsion de sécurité négative le raménera en S, et la prochaine impulsion de commande normale se présentera comme incorrecte, ce qui déclenchera les deux impulsions de rattrapage comme cela a été expliqué plus haut. Une impulsion de sécurité positive amènera le rotor en S2; dans ce cas, la prochaine impulsion de commande se présentera comme correcte et aucun rattrapage n'aura lieu. Dans la pratique, on préférera une impulsion de sécurité négative car il faut moins d'énergie pour amener le rotor de la position 11 à la position S, que de la position I1 à la position S2. Dans un exemple de réalisation de l'invention, on choisit pour Ts une durée comprise entre 0,2 et 0,5 ms et pour le laps de temps séparant la fin de l'impulsion de commande de l'impulsion de sécurité une durée de l'ordre de 50 ms.FIG. 6 shows an arrangement which overcomes the drawback cited by proposing, according to a particular embodiment of the invention, to send to the motor coil a predetermined period of time after the end of the duration control pulse T t , a safety pulse of duration T S. If we refer again to FIG. 5, it will be understood that, if the rotor is locked in position 11 , a pulse of very short duration will suffice to send it either to S 1 or to S 2 . A negative safety pulse will bring it back to S, and the next normal command pulse will show up as incorrect, which will trigger the two catch-up pulses as explained above. A positive safety pulse will bring the rotor to S 2 ; in this case, the next command pulse will appear to be correct and no catch-up will take place. In practice, a negative safety pulse will be preferred since it takes less energy to bring the rotor from position 1 1 to position S, than from position I 1 to position S 2 . In an exemplary embodiment of the invention, a duration between 0.2 and 0.5 ms is chosen for T s and for the period of time separating the end of the control pulse from the safety pulse a duration of the order of 50 ms.

On vient d'expliquer comment les diverses impulsions de commande sont arrangées les unes par rapport aux autres, comment leurs durées s'adaptent à la charge présentée par le mécanisme et comment il convient de rattraper les pas perdus. Ceci présuppose naturellement qu'on dispose de moyens pour détecter les pas qui n'ont pas été franchis. Dans la demande EP-A-0 022 270, on base cette détection sur la polarité de l'impulsion de commande par rapport à la position du rotor et, si le moteur est du type à entrefer, on mesure la tension induite Ui recueillie aux bornes de la bobine, cette dernière étant mise en circuit ouvert. Si le moteur reçoit une impulsion dirigée dans le bon sens, on mesure une tension induite Ui de grande amplitude alors que cette tension est nulle, voire négative si l'impulsion est dirigée dans le mauvais sens. On a exposé dans le préambule l'inconvénient qu'il y avait à mesurer cette tension à circuit ouvert pour un moteur qui présente des zones saturables puisque l'amplitude de ladite tension est relativement faible.We have just explained how the various control pulses are arranged in relation to each other, how their durations adapt to the load presented by the mechanism and how it is necessary to make up for lost steps. This naturally presupposes that we have means to detect the steps that have not been taken. In application EP-A-0 022 270, this detection is based on the polarity of the control pulse with respect to the position of the rotor and, if the motor is of the air gap type, the induced voltage Ui collected at the coil terminals, the latter being placed in open circuit. If the motor receives a pulse directed in the right direction, a large amplitude induced voltage Ui is measured while this voltage is zero, or even negative if the pulse is directed in the wrong direction. We set out in the preamble the disadvantage that there was to measure this open circuit voltage for a motor which has saturable zones since the amplitude of said voltage is relatively low.

La figure 7 montre le dispositif mis en oeuvre pour obtenir une tension Ui très confortable même si le moteur est du type à zones saturables. Un tel dispositif a été décrit dans le document FR-A-2 388 326 cité dans le rapport de recherche. Ce dispositif comprend un pont à quatre branches dont chacune comporte un interrupteur, la première diagonale du pont recevant une source d'alimentation continue et la seconde comportant la bobine du moteur. Une résistance est disposée en série avec cette bobine et est pontée par un dispositif interrupteur. Des moyens sont mis en action pour ouvrir ledit dispositif quand on doit détecter la rotation ou l'absence de rotation du rotor.FIG. 7 shows the device used to obtain a very comfortable voltage Ui even if the motor is of the type with saturable zones. Such a device has been described in document FR-A-2 388 326 cited in the research report. This device comprises a bridge with four branches, each of which comprises a switch, the first diagonal of the bridge receiving a continuous power source and the second comprising the motor coil. A resistor is arranged in series with this coil and is bridged by a switching device. Means are put into action to open said device when it is necessary to detect the rotation or the absence of rotation of the rotor.

Le schéma de la figure 7 présente une résistance 40 branchée en série avec la bobine 15 du moteur, résistance qui peut être court-circuitée lorsqu'on ferme l'interrupteur 35. Dans ce schéma, on trouve entre les bornes référencées 41 et 42 des impulsions de commande alternées d'amplitude U en provenance de la source d'alimentation continue Up livrée par la pile lorsque les interrupteurs 31-32, respectivement 33-34 sont fermés. Si l'on définit par TRB la durée pendant laquelle la seule bobine 15 est branchée aux bornes 41 et 42, par Tx la durée pendant laquelle l'ensemble bobine 15 - résistance 40 est branché auxdites bornes et par Tcc la durée pendant laquelle la bobine 15 est mise en court-circuit, la séquence de commande des interrupteurs s'établit selon le tableau ci-après pour une impulsion positive:

Figure imgb0001
The diagram in FIG. 7 shows a resistor 40 connected in series with the coil 15 of the motor, a resistor which can be short-circuited when the switch 35 is closed. In this diagram, there are between the terminals referenced 41 and 42 alternating control pulses of amplitude U coming from the continuous power source Up delivered by the battery when the switches 31-32, respectively 33-34 are closed. If we define by T RB the duration during which the only coil 15 is connected to terminals 41 and 42, by T x the duration during which the coil 15 - resistor 40 assembly is connected to said terminals and by Tcc the duration during which coil 15 is short-circuited, the switch control sequence is established according to the table below for a positive pulse:
Figure imgb0001

Dans les techniques actuelles, se sont des transistors qui jouent le rôle des interrupteurs. lls reçoivent leurs signaux d'un circuit de mise en forme classique.In current techniques, transistors play the role of switches. They receive their signals from a conventional shaping circuit.

On se reportera maintenant à la figure 8 pour comprendre le rôle joué par la résistance additionnelle 40. Dans ce graphique, on a représenté en trait plein l'impulsion de commande U qu'on trouve aux bornes 41 et 42 (voir figure 7). Cette impulsion de commande est présente tant que les interrupteurs 31 et 32 sont fermés, c'est-à-dire pendant la période TR8 et la période Tx (voir tableau ci-dessus). On désigne la durée de cette impulsion par Tn. Pendant la période TRB, la résistance 40 est court-circuitée et la bobine 15 reçoit une tension UB, représentée en traits interrompus, identique à la tension U si l'on fait abstraction de la faible chute de tension qui existe aux bornes de l'interrupteur 35. Cette tension UB est aussi à peu de chose près celle que l'on trouve aux bornes de la pile (Up). UB est la tension motrice seule utile à entraîner le rotor. Pendant la période TX, la résistance 40 est branchée en série avec la bobine 15, l'interrupteur 35 est ouvert. C'est la période de mesure destinée à prélever aux bornes de la bobine la tension induite Ui développée par le moteur.We will now refer to FIG. 8 to understand the role played by the additional resistor 40. In this graph, we have shown in solid lines the control pulse U which is found at terminals 41 and 42 (see FIG. 7). This control pulse is present as long as the switches 31 and 32 are closed, that is to say during the period TR8 and the period T x (see table above). The duration of this pulse is designated by T n . During the period T RB , the resistor 40 is short-circuited and the coil 15 receives a voltage U B , shown in broken lines, identical to the voltage U if we disregard the low voltage drop which exists across the terminals of the switch 35. This voltage U B is also about the same as that found at the terminals of the battery (Up). U B is the only driving voltage useful to drive the rotor. During the period T X , the resistor 40 is connected in series with the coil 15, the switch 35 is open. It is the period of measurement intended to take at the terminals of the coil the induced voltage Ui developed by the motor.

La figure 9 représente le comportement du moteur pendant la période de mesure TX. On s'y référera en même temps qu'aux figures 7 et 8. On l'a déjà dit, dés le début de la période Tx, la tension de commande U est appliquée aux bornes 41 et 42 du circuit qui comprend la bobine 3 et la résistance 40 connectées en série. On choisit la valeur de la résistance 40 de manière à engendrer dans la bobine 3 un courant lSAT qui, à son tour, va produire un flux Φb suffisant pour saturer les isthmes 4 du stator. Dès l'instant où ces isthmes sont saturés, la quasi totalité du flux Φab créé par l'aimant passe par le noyau de la bobine 3. Le flux Φb produit aux bornes de la bobine une tension induite

Figure imgb0002
où Nb représente le nombre de spires de la bobine. On se retrouve ainsi dans des conditions semblables à celles qui ont été décrites dans la demande EP-A-0 022 270 dans laquelle à une tension Ui importante correspond l'application d'une impulsion de polarité correcte au moteur. Cette situation est illustrée sur la figure 8 qui montre qu'à un moment prédéterminé tx de la période Tx, la tension Ui, représentée en traits interrompus, est de grande amplitude en suite de quoi on continuera à alimenter le moteur avec les mêmes impulsions de commande de largeur Tn. En pratique, on mesurera la tension induite Ui dans un intervalle TUi compris dans la période Tx, intervalle qui peut embrasser, par exemple, les deux derniers tiers de la période TX. La figure 8 montre aussi que le courant lSAT pendant la période de mesure Tx est de faible amplitude bien que suffisante cependant pour saturer les isthmes. Cet artifice qui consiste à brancher une résistance en série avec la bobine du moteur ne consomme donc qu'une énergie négligeable puisque le courant nécessaire est très faible et que la durée pendant laquelle ce courant est développé est réduite à une faible fraction de la durée totale de l'impulsion de commande. Enfin, pendant le temps qui sépare la fin de l'impulsion de commande et l'arrivée d'une nouvelle impulsion, la bobine est court-circuitée, comme c'est l'usage habituellement pour amortir le mouvement du rotor.FIG. 9 represents the behavior of the motor during the measurement period T X. We will refer to this at the same time as in FIGS. 7 and 8. We have already said it, from the start of the period T x , the control voltage U is applied to the terminals 41 and 42 of the circuit which comprises the coil 3 and the resistor 40 connected in series. The value of the resistance 40 is chosen so as to generate in the coil 3 a current l SAT which, in turn, will produce a flux Φ b sufficient to saturate the isthms 4 of the stator. As soon as these isthmus are saturated, almost all of the flux Φ ab created by the magnet passes through the core of the coil 3. The flux Φ b produces across the coil an induced voltage
Figure imgb0002
 where N b represents the number of turns of the coil. We thus find ourselves in conditions similar to those which have been described in application EP-A-0 022 270 in which a high voltage Ui corresponds to the application of a pulse of correct polarity to the motor. This situation is illustrated in FIG. 8 which shows that at a predetermined time t x of the period T x , the voltage Ui, shown in dashed lines, is of large amplitude as a result of which the motor will continue to be supplied with the same width control pulses T n . In practice, the induced voltage Ui will be measured in an interval T Ui included in the period T x , interval which can embrace, for example, the last two thirds of the period T X. FIG. 8 also shows that the current l SAT during the measurement period T x is of small amplitude although sufficient however to saturate the isthmus. This device which consists in connecting a resistor in series with the motor coil therefore consumes only negligible energy since the necessary current is very low and the time during which this current is developed is reduced to a small fraction of the total time of the command pulse. Finally, during the time between the end of the control pulse and the arrival of a new pulse, the coil is short-circuited, as is customary to dampen the movement of the rotor.

Comme on le verra plus loin, la méthode qui vient d'être décrite ne convient que pour des impulsions de commande dont la durée Tn est relativement courte. Ceci étant, on peut résumer ce qui vient d'être dit en affirmant que, pour des impulsions de commande dont la largeur est égale ou inférieure à la durée Tn, on branche une résistanceen série avec la bobine du moteur pendant une période Tx située immédiatement avant la fin de l'impulsion de commande U et qu'on mesure durant ladite période Tx pendant un intervalle prédéterminé Tuila tension induite aux bornes de la bobine du moteur.As will be seen below, the method which has just been described is suitable only for control pulses whose duration T n is relatively short. That said, we can summarize what has just been said by asserting that, for control pulses whose width is equal to or less than the duration T n , a resistor is connected in series with the motor coil during a period T x located immediately before the end of the control pulse U and which is measured during said period T x during a predetermined interval Tuila induced voltage at the terminals of the motor coil.

Pour donner un exemple pratique, on choisit pour la période TRB la plus courte une durée de 3 ms et pour la période Tx une durée de 1 ms tandis que la valeur de la résistance 40 est de 15 kQ pour une résistance de la bobine de 3 kQ.To give a practical example, we choose for the shortest TRB period a duration of 3 ms and for the period T x a duration of 1 ms while the value of the resistance 40 is 15 kQ for a resistance of the coil. 3 kQ.

Si le procédé qui vient d'être décrit a spécialement été développé pour un moteur à zones saturables, il pourrait aussi être appliqué à un moteur à entrefers bien que cela pourrait être ressenti comme un luxe inutile puisqu'il suffit, comme on l'a dit, de mesurer pour ce dernier type de moteur la tension Ui immédiatement après la fin de l'impulsion UB, la bobine étant disposée à circuit ouvert. Cependant l'universalité du procédé permettrait d'utiliser le même circuit électronique de commande pour les deux types de moteur, ce qui irait dans le sens d'une simplification et d'une diminution de prix de revient.If the process which has just been described has been specially developed for an engine with saturable zones, it could also be applied to an engine with air gaps although this could be felt as an unnecessary luxury since it suffices, as we have said, to measure for this latter type of motor the voltage Ui immediately after the end of the pulse U B , the coil being arranged in open circuit. However, the universality of the process would make it possible to use the same electronic control circuit for the two types of engine, which would go in the direction of a simplification and a reduction in cost price.

On vient d'expliquer comment on mesure la tension induite Ui aux bornes de la bobine du moteur en saturant préalablement ses isthmes si l'on a affaire à un moteur à zones saturables. On a rappelé également l'enseignement de la demande EP-A-0 022 270 où cette tension induite est mesurée immédiatement après l'impulsion motrice, la bobine étant disposée à circuit ouvert. On a expliqué dans la demande citée que la tension Ui est égale à

Figure imgb0003
où Q est la vitesse angulaire du rotor et Cab/i est le facteur de couplage. Si l'on se reporte encore une fois à la figure 5, on se rend compte qu'au-delà d'une certaine position angulaire correspondant à une durée d'impulsion limite la tension Ui se situera audessous d'une valeur exploitable puisque le facteur de couplage Cab/i diminue. Or, comme il est nécessaire d'augmenter la durée des impulsions de commande si l'on désire augmenter le couple mécanique que pourra fournir le moteur, il arrivera bien un moment où la durée de l'impulsion de commande sera trop longue pour que la bobine puisse fournir une tension de détection qui soit encore exploitable.We have just explained how the induced voltage Ui is measured across the motor coil by saturating its isthmus beforehand if we are dealing with a motor with saturable zones. We also recalled the teaching of application EP-A-0 022 270 where this induced voltage is measured immediately after the driving pulse, the coil being arranged in open circuit. It was explained in the cited application that the voltage Ui is equal to
Figure imgb0003
 where Q is the angular speed of the rotor and Cab / i is the coupling factor. If we refer once again to FIG. 5, we realize that beyond a certain angular position corresponding to a pulse duration limits the voltage Ui will be below an exploitable value since the Cab / i coupling factor decreases. However, since it is necessary to increase the duration of the control pulses if it is desired to increase the mechanical torque which the motor can supply, there will come a point when the duration of the control pulse will be too long for the coil can supply a detection voltage which is still usable.

La figure 10 illustre le phénomène qui vient d'être expliqué et montre comment diminue l'amplitude de la tension Ui lorsque l'impulsion UB s'allonge. On constate qu'aux impulsions motrices de durée croissante UB1, UB2 et UB3 correspondent respectivement les tensions induites Ui1, Ui2 et Ui3, le maximum desdites tensions se situantsur une enveloppe dont l'allure est représentative du facteur de couplage Cab/i, à la vitesse près. Pour l'impulsion U84, la figure montre qu'aucune tension induite n'est détectée. Si l'on admet que la tension induite Ui3 suivant l'impulsion UB3 est déjà impropre à faire fonctionner correctement le circuit de réglage puisqu'elle présente une faible amplitude, il faudra avoir recours à un artifice qui permette une détection sùre pour toutes les impulsions de commande dont la largeur dépasse la durée limite Tn.FIG. 10 illustrates the phenomenon which has just been explained and shows how the amplitude of the voltage Ui decreases when the pulse U B lengthens. It can be seen that the driving pulses of increasing duration U B1 , U B2 and U B3 correspond respectively to the induced voltages Ui 1 , Ui 2 and Ui 3 , the maximum of said voltages being located on an envelope whose shape is representative of the coupling factor. Cab / i, down to speed. For the U 84 pulse, the figure shows that no induced voltage is detected. If it is admitted that the induced voltage Ui 3 following the pulse U B3 is already unsuitable for making the adjustment circuit work correctly since it has a low amplitude, it will be necessary to have recourse to a device which allows safe detection for all control pulses whose width exceeds the limit duration Tn.

La figure 11 montre comment on procède selon un mode particulier de réalisation de l'invention pour palier l'inconvénient cité. Dans ce graphique, l'impulsion de commande U est composée de deux impulsions motrices UB et Uc séparéespar une période Tx pendant laquelle on mesure la tension induite selon le procédé qui a été expliqué plus haut. Ainsi, si la largeur Tt del'impulsion de commande U est supérieure à la durée Tn à partir de laquelle l'amplitude de la tension induite Ui serait insuffisante ou nulle, on mesure ladite tension induite Ui pendant un intervalle TUi compris dans la période Tx précédant immédiatement la fin de la période Tn. En d'autres termes, si la durée Tt de l'impulsion U nécessaire à faire progresser le rotor est trop longue pour qu'on puisse détecter une tension induite d'amplitude suffisante, comme cela a été expliqué plus haut, on ouvre une fenêtre dans ladite impulsion U et on mesure dans cette fenêtre la tension induite. Il va de soi que l'emplacement de cette fenêtre est choisi en un endroit où l'amplitude de la tension induite est encore importante. Cette fenêtre est réalisée en branchant une résistance en série avec la bobine pendant la période Tx (résistance 40 de la figure 7) s'il s'agit d'unmoteur à zones saturables (figure 2). Dans ce cas, la séquence de commande des interrupteurs montrés enfigure 7 s'établit selon le tableau ci-dessous:

Figure imgb0004
Figure 11 shows how we proceed according to a particular embodiment of the invention to overcome the drawback mentioned. In this graph, the control pulse U is composed of two driving pulses U B and U c separated by a period T x during which the induced voltage is measured according to the method which has been explained above. Thus, if the width T t of the control pulse U is greater than the duration T n from which the amplitude of the induced voltage Ui would be insufficient or zero, said induced voltage Ui is measured during an interval T Ui included in the period T x immediately preceding the end of the period T n . In other words, if the duration T t of the pulse U necessary to make the rotor advance is too long for an induced voltage of sufficient amplitude to be detected, as has been explained above, one opens a window in said pulse U and the induced voltage is measured in this window. It goes without saying that the location of this window is chosen in a place where the amplitude of the induced voltage is still large. This window is produced by connecting a resistor in series with the coil during the period T x (resistor 40 in FIG. 7) if it is a motor with saturable zones (FIG. 2). In this case, the command sequence of the switches shown in Figure 7 is established according to the table below:
Figure imgb0004

Il faut mentionner que la méthode avec fenêtre convient aussi parfaitement si on l'applique à un moteur avec entrefers (voir figure 1 ) où le phénomène d'extinction de la tension induite existe également quand l'impulsion de commande s'allonge. Dans ce cas, on peut très bien ne rien changer au schéma de la figure 7 et à la séquence du tableau ci-dessus si l'on veut utiliser une électronique de commande commune aux deux types de moteur. Mais on peut aussi disposer la bobine du moteur à circuit ouvert, comme cela est préconisé dans la demande EP-A-0 022 270, quand on veut mesurer la tension induite. Si tel est le cas, on supprimera la résistance 40 et l'interrupteur 35 representés en figure 7 et on ouvrira tous les interrupteurs 31 à 34 pendant la fenêtre de mesure de durée TX. Il faut dire encore que si on mesure la tension Ui à circuit ouvert dans le moteur à entrefers, le graphique de la figure 11 reste le même sauf en ce qui concerne le courant i qui s'annule pendant la période TX.It should be mentioned that the window method is also perfectly suitable if it is applied to a motor with air gaps (see Figure 1) where the phenomenon of extinction of the induced voltage also exists when the control pulse lengthens. In this case, we can very well not change anything in the diagram in Figure 7 and in the sequence of the table above if we want to use control electronics common to both types of engine. However, the coil of the motor with an open circuit can also be placed, as recommended in application EP-A-0 022 270, when it is desired to measure the induced voltage. If this is the case, the resistor 40 and the switch 35 shown in FIG. 7 will be deleted and all the switches 31 to 34 will be opened during the duration measurement window T X. It must also be said that if the open circuit voltage Ui is measured in the air gap motor, the graph in FIG. 11 remains the same except for the current i which is canceled out during the period T X.

La figure 12 illustre de façon exemplaire comment on adapte la largeur de l'impulsion de commande à la charge imposée au moteur et à quel moment on mesure la tension induite. Pour la construction donnée en exemple, il a été établi que cette tension induite est encore suffisante si on la mesure pendant une période Tx = 1 ms précédant immédiatement la fin de l'impulsion de commande dont la durée est égale ou inférieure à Tn = 5 ms. Du niveau 1 où la charge est la plus faible au niveau 3 où elle est légèrement plus élevée, la durée de l'impulsion de commande passe de 4 à 5 ms. La mesure de la tension induite se fait immédiatement avant la fin de l'impulsion de commande puisque la durée de ladite impulsion est égale (niveau 3) ou inférieure (niveaux 1 et 2) à la durée Tn. On voit que pour les mêmes niveaux, la durée TRB de l'impulsion motrice UB passe de 3 à 4 ms. A partirdu niveau 4 adapté à une charge plus importante et jusqu'au niveau 6 correspondant à la charge maximum que peuvent présenter toutes les contraintes réunies ensemble, la durée de l'impulsion de commande passe de 6,5 à 10 ms. La mesure de la tension induite doit se faire dans une fenêtre Tx car, à partir du niveau 4, la largeur de l'impul- sion de commande est supérieure à la durée prédéterminée Tn. Dans ces trois derniers niveaux, la fenêtre sépare les deux impulsions motrices Ua et Uc dont la première est de durée constante TRB = 4 ms et dont la seconde Tc est de 1,5,3 et 5 ms quand ont passe du niveau 4 au niveau 6. La figure 12 montre aussi l'impulsion de rattrapage de durée T, dont la largeur est choisie à 8 ms.FIG. 12 illustrates in an exemplary manner how the width of the control pulse is adapted to the load imposed on the motor and when the induced voltage is measured. For the example construction, it has been established that this induced voltage is still sufficient if it is measured for a period Tx = 1 ms immediately preceding the end of the control pulse whose duration is equal to or less than Tn = 5 ms. From level 1 where the load is weakest to level 3 where it is slightly higher, the duration of the control pulse goes from 4 to 5 ms. The measurement of the induced voltage is made immediately before the end of the control pulse since the duration of said pulse is equal (level 3) or less (levels 1 and 2) to the duration Tn. We see that for the same levels, the duration T RB of the driving pulse U B goes from 3 to 4 ms. From level 4 adapted to a higher load and up to level 6 corresponding to the maximum load that all the stresses put together can present, the duration of the control pulse increases from 6.5 to 10 ms. The measurement of the induced voltage must be done in a window T x because, from level 4, the width of the control pulse is greater than the predetermined duration T n . In these last three levels, the window separates the two driving pulses U a and U c , the first of which is of constant duration T RB = 4 ms and the second of which T c is 1.5.3 and 5 ms when the level 4 to level 6. Figure 12 also shows the catch-up pulse of duration T, the width of which is chosen at 8 ms.

L'invention qui vient d'être décrite poursuit le même but que celui qui a été expliqué dans la demande EP-A-0 022 270, à savoir proposer une méthode qui détecte un signal de tension induite de grande amplitude lorsque la bobine du moteur reçoit une impulsion de polarité correcte. Cette méthode conduit à un fonctionnement très sûr du système d'asservissement qui répond par oui ou non, comme c'est le cas dans un système logique.The invention which has just been described pursues the same aim as that which was explained in application EP-A-0 022 270, namely to propose a method which detects a signal of induced voltage of large amplitude when the motor coil receives a correct polarity pulse. This method leads to a very safe operation of the servo system which responds with yes or no, as is the case in a logic system.

Par ailleurs, comme cela a été exposé à propos de la demande EP-A-0 022 270, la tension Ui est comparée à une tension de référence dans un comparateur. Si Ui est plus grand que ladite référence, c'est une impulsion de polarité correcte qui a été envoyée au moteur et il n'apparaît aucun signal à la sortie du comparateur. Le circuit de commande continue à envoyer des impulsions de même durée. Si, au contraire, Ui est plus petit que la référence, c'est une impulsion de polarité incorrecte qui a été envoyée au moteur et il apparaît un signal à la sortie du comparateur qui oblige le circuit de commande à envoyer deux impulsions de rattrapage puis un train d'impulsions de commande, comme cela a été expliqué ci-dessus.Furthermore, as explained in connection with application EP-A-0 022 270, the voltage Ui is compared with a reference voltage in a comparator. If Ui is greater than said reference, a pulse of correct polarity has been sent to the motor and no signal appears at the output of the comparator. The control circuit continues to send pulses of the same duration. If, on the contrary, Ui is smaller than the reference, an incorrect polarity pulse has been sent to the motor and a signal appears at the output of the comparator which forces the control circuit to send two catching pulses then a control pulse train, as explained above.

Claims (6)

1. Method for slaving a stepping motor driven by a train of bipolar control pulses to the load imposed by a timepiece mechanism, the beginning of one of said control pulses being separated from the next following control pulse by a predetermined time lapse in which method there is measured at the motor winding terminals the induced voltate Ui generated by rotation of the rotor in response to one of said control pulses n of duration T1 whence if such voltage is less than a predetermined threshold there is applied to the motor following said pulse n a first group of two bipolar recovery pulses of long duration Ta following which the motor is driven from the control pulse n + 1 on by control pulses of duration T2 where T2 > T1 characterized in that the duration of the control pulses is adjusted to the load by successive increasing levels when the load increases in the following manner: the voltage Ui induced in response to control pulse n + 2 is measured and if such voltage is less than said predetermined threshold there is applied to the motor following said pulse n + 2 a second group of said two recovery pulses following which the motor is driven from the control pulse n + 3 on by control pulses of duration T3 where T3 < T2 the method being thus continued; and in that in order to measure the induced voltage Ui a resistance is connected in series with the motor winding during a period Tx, the voltage Ui induced in a predetermined interval TUi included in the period Tx is measured said period Tx being located either immediately before the end of the control pulse if the duration of the latter is equal to or less than a predetermined duration Tn, or in a position preceding by a certain interval the end of the predetermined duration Tn if the duration of the control pulse is greater than said predetermined duration Tn.
2. Method for slaving a stepping motor driven by a train of bipolar control pulses to the load imposed by a timepiece mechanism, the beginning of one of said controlpulses being separated from the next following control pulse by a predetermined time lapse in which method there is measured at the motor winding terminals the induced voltage Ui generated by rotation of the rotor in response to one of said control pulses n of duration T, whence if such voltage is less than a predetermined threshold there is applied to the motor following said pulse n a first group of two bipolar recovery pulses of long duration Ta following which the motor is driven from the control pulse n + 1 on by control pulses of duration T2 characterized in that the voltage Ui induced in response to the control pulse n + 2 is measured and if such voltage is less than said predetermined threshold, following said pulse n + 2, there is applied to the motor a second group of said two recovery pulses following which the motor is driven from the control pulse n + 3 on by control pulses of duration T3, the method being thus continued, the durations T2, T3 etc. being equal to T1 so long as a given number of recovery pulses has not been counted in a second predetermined lapse of time, the duration of the control pulses increasing relative to the duration of the preceding control pulses in the case where it has been detected that the given number of recovery pulses has been attained in said second predetermined lapse of time; and in that, in order to measure the induced voltage Ui, a resistance is connected in series with the motor winding during a period Tx, the voltage Ui induced in a predetermined interval TUi included in the period Tx is measured, said period Tx being located either immediately before the end of the control pulse if the duration of the latter is equal to or less than a predetermined duration Tn or in a position preceding by a certain interval the end of the predetermined duration Tn if the duration of the control pulse is greater than said predetermined duration Tn.
3. Method according to claim 1 or claim 2 characterized in that there is applied to the motor winding, another predetermined time lapse after the end of each control pulse, a security pulse of duration Ts such that if the rotor stalls in mid course at a position of unstable equilibrium it brings said rotor to one of its immediately neighbouring equilibrium positions.
4. Method according to claim 3 characterized in that said security pulse has its polarity inverted relative to the polarity of the preceding control pulse.
5. Method according to claim 1 characterized in that the duration of the control pulses is adjusted to the load by successive diminishing levels when the load decreases.
6. Method according to claim 5 characterized in that if, following the presence of an induced voltage Ui greater than the predetermined threshold no failure of rotation of the rotor is detected over a predetermined period the duration of the control pulses is lowered by a level the method being thus continued.
EP82102626A 1981-03-31 1982-03-29 Method of controlling a stepping motor Expired EP0062273B1 (en)

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CH2165/81 1981-03-31
CH216581A CH644983GA3 (en) 1981-03-31 1981-03-31

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CH649187GA3 (en) * 1982-10-13 1985-05-15
JPS5980147A (en) * 1982-10-29 1984-05-09 Rhythm Watch Co Ltd Small motor for timepiece
JPH0681551B2 (en) * 1984-10-16 1994-10-12 セイコ−電子工業株式会社 Rotation detection method for step motor
JP3299756B2 (en) * 1993-01-18 2002-07-08 セイコーインスツルメンツ株式会社 Electronic clock

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US4158287A (en) * 1976-08-12 1979-06-19 Citizen Watch Company Limited Driver circuit for electro-mechanical transducer
JPS5385467A (en) * 1976-12-30 1978-07-27 Seiko Epson Corp Electronic wristwatch
JPS53132385A (en) * 1977-04-23 1978-11-18 Seiko Instr & Electronics Ltd Electronic watch
JPS5477169A (en) * 1977-12-02 1979-06-20 Seiko Instr & Electronics Ltd Electronic watch
CH625384B (en) * 1977-12-20 Ebauches Electroniques Sa STEP MOTOR NON-ROTATION DETECTION DEVICE FOR CLOCKWORK PART AND LOST STEPS CATCHING UP.
FR2461399A1 (en) * 1979-07-09 1981-01-30 Suisse Horlogerie POSITION DETECTOR OF A STEP BY STEP MOTOR

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DE3272080D1 (en) 1986-08-28

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