EP0021320A1 - Operation detector for a stepping motor - Google Patents

Abstract

Feeding device for detecting the advance of a stepping motor and sending to said motor a train of long duration pulses if a step has not been taken in response to a short duration pulse. The detector comprises means for taking a first signal developed by the current in the motor coil (22) and for creating a second signal which is the integral of the first in order to detect whether the motor has taken its step in the not. The invention applies to micromotors for timepieces.

Description

The subject of the present invention is a device for supplying a single-phase stepping motor for a timepiece arranged to control the running of the motor by a first type of bipolar pulses of small width or by a second type of pulses. bipolar of greater width, a train of said second type of pulses being sent to the motor if the latter has not progressed by one step in response to said first type of pulses.

A control device of this type is known. The German presentation DEOS 27 45 052 describes a control system which applies a low energy signal to the motor if the motor load is low and a high energy signal if the motor load is high, with the aim of reducing d 'about 60% of the watch's energy consumption. The cited invention bases the passage from the first signal to the second signal on the observation of the shape of the motor current, the maxima of which move to the right when the load of the motor increases. By detecting the position of the maxima, it is thus possible to send a large control pulse (eg 7.8 ms) to the motor when the mechanical torque increases, which is the case for example at the time of loading. of the calendar date. This system has the disadvantage of not being able to know if, as a result of the control pulse, the motor has advanced by one step. There may then be circumstances where a train of very large pulses is sent to the motor without any need.

Another control device is described in patent applications FR 2 384 289 and FR 2 388 323 where this time the detection of the pitch is provided. In the cited patents, the configuration of the engine is such that it has a saturable zone. In these circumstances, a so-called detection pulse of the order of a millisecond makes it possible to detect whether the rotor has rotated or not. If the step has not been taken, a correction pulse (7.8 ms) is immediately sent to the motor to replace the normal pulse (3.9 ms). As already mentioned, this system requires a saturable area motor and therefore has the drawback of not being applicable to all stepper motors known to the watch industry. On the other hand, it should be noted that the detection voltage goes from simple to double when the motor takes its step. The present invention provides a much larger difference, which gives it better operational reliability, as explained below.

Let us also cite the brief exposed CH 13 723/72 which proposes the differentiation of the detection signal and the elongation of the control pulse as a function of the mechanical load applied to the motor. This system has the disadvantage that the detection of the maximum speed of the rotor does not necessarily mean that said rotor has taken a step as will appear in the explanations which follow.

Finally, US patent 4,114,364 also proposes to lengthen the control pulse in response to the load of the motor. Besides the fact that the system does not detect the rotation of the rotor, it has the drawback of high consumption, which is not the objective set.

It is the object of the invention to eliminate the above drawbacks and to provide a control device which saves the energy of the power source while being very safe in its operation.

dont la valeur indique si le moteur a progressé d'un pas en réponse à une impulsion de faible largeur.The power supply device according to the invention is characterized in that it comprises a step detector comprising first means for taking a first signal Ud developed by the current which flows through the coil of said motor and second means for creating a second signal

the value of which indicates whether the motor has advanced one step in response to a narrow pulse.

• La figure 1 est l'organigramme d'une alimentation avec contrôle du pas.
• La figure 2 représente les divers signaux appliqués au moteur.
• La figure 3 montre l'allure du couple mutuel, du couple de positionnement et du flux mutuel aimant - bobine en fonction de la position du rotor.
• La figure 4a montre le schéma de principe du détecteur de position selon l'invention.
• La figure 4b montre une variante du schéma de principe du détecteur de position selon l'invention.
• La figure 5 montre l'allure de la tension à la sortie de l'intégrateur et du courant dans la bobine quand le rotor a franchi son pas.
• La figure 6 montre l'allure de la tension à la sortie de l'intégrateur et du courant dans la bobine quand le rotor n'a pas franchi son pas.

The invention will be better understood in the light of the description which follows and of the drawings which represent the operation of the engine and of its control device.

• Figure 1 is the flow diagram of a power supply with pitch control.
• Figure 2 shows the various signals applied to the motor.
• FIG. 3 shows the shape of the mutual torque, the positioning torque and the mutual magnet-coil flow as a function of the position of the rotor.
• Figure 4a shows the block diagram of the position detector according to the invention.
• FIG. 4b shows a variant of the block diagram of the position detector according to the invention.
• FIG. 5 shows the shape of the voltage at the output of the integrator and of the current in the coil when the rotor has passed its pitch.
• FIG. 6 shows the shape of the voltage at the output of the integrator and of the current in the coil when the rotor has not crossed its pitch.

The invention which will be described aims firstly at reducing the consumption of the timepiece. In fact, it can be seen that a watch micromotor generally works practically empty. However, to ensure proper operation in special cases such as temperature variation, external magnetic field, shock, angular acceleration, etc., it is necessary to supercharge it, which leads to unnecessary consumption of the battery energy. The invention proposes a new device for controlling the pitch of the motor which makes it possible to adapt, with large safety margins, the supply as a function of the load, from which it results an appreciable gain in energy consumption.

The general principle of supplying the motor as already mentioned in certain patents cited above is represented in FIG. 1 which is a supply flow diagram with pitch control. The motor is normally supplied by short duration pulses (eg 6 ms) emitted by the generator 1. A position detector 2, object of the present invention and which will be described in detail later, makes it possible to check whether the motor has made its move. If so, the decision-making body 3 has given line 4 to generator 1 that it must continue to supply the engine. If not, the same decision-making unit controls, via line 5, the generator 6 which emits long duration pulses (eg 8 ms) which supply the motor and replace the short duration pulses. This substitutionalieu for a time of n seconds fixed by the counter 7. After this lapse of time, the motor is again supplied by short duration pulses. It can be seen that the motor is supplied alternately and as required either by loop 8 giving short duration pulses, the detector being in operation, or by loop 9 giving long duration pulses for a time determined by the counter, the detector off. The various anomalies which may arise during operation due to the causes mentioned above last for a certain time. It will therefore be understood that systematically sending a long pulse after each short pulse which has failed to advance the motor by one step would be expensive in terms of energy consumed and contrary to the aim which the invention proposes to achieve. The duration during which the long pulses are sent to the motor is of the order of 5 minutes, but other values could be chosen.

FIG. 2a represents the train of short pulses which is sent to the motor when the latter takes its step. The pulses 10, bipolar and with a duration of the order of 6 ms, are emitted every second by the generator 1. FIG. 2b represents the long pulse train 11 with a duration of the order of 8 ms emitted by the generator 6, pulses succeeding each other at a rate of one second. For the reasons which will be explained later, the start of the long pulse is offset by 40 ms with respect to the start of the short pulse and when the position detector, after pulse 12 shown in FIG. 2c, detects an absence of rotation, the train of long pulses 13 is sent to the motor for approximately 5 minutes, after which the motor is switched again to the short pulses 14.

FIG. 3 represents the value of the couples C which act on the rotor as a function of its angle of rotation α. As is known, the rotor of the stepping motor is subjected to two kinds of torques: a static holding torque Ca due to the magnet alone and a dynamic torque Cab motor due to the interaction of the flux of the magnet with the flow of the coil when it is supplied. Initially the rotor is in position S _l . If an impulse is sent to the motor and it takes its step, i1 will find itself in position S ₂ . In the same FIG. 3, the value of the mutual flux magnet - coil 4j is shown as a function of the angle of rotation of the rotor. The present invention is precisely based on the value of this flux which takes different values depending on whether the motor has progressed by one step or not.

dans laquelle

• U = tension aux bornes du moteur,
• R = résistance totale du circuit,
• L = inductance de la bobine,
• i = courant dans la bobine,
• Ψ = flux mutuel aimant - bobine.

En intégrant entre 0 et T l'équation ci-dessus, on obtient :

En choisissant un temps T plus grand que la longueur d'impulsion, parexem- ple 30 ms, tout courant aura cessé dans la bobine du moteur, ce qui fait que i (T) = 0. D'autre part, en observant la valeur que peut prendre le flux présenté en figure 3, on s'aperçoit que :

• 
  si le moteur a fait son pas, et
  
• si le moteur n'a pas fait son pas, si bien que la relation (2) devient :
  
• si le moteur a fait son pas, et
• si le moteur n'a pas fait son pas.

The differential equation of the voltage collected at the terminals of a micro-motor can be written:

in which

• U = voltage across the motor,
• R = total resistance of the circuit,
• L = inductance of the coil,
• i = current in the coil,
• Ψ = mutual flux magnet - coil.

By integrating between 0 and T the above equation, we obtain:

By choosing a time T greater than the pulse length, for example 30 ms, all current will have stopped in the motor coil, which means that i (T) = 0. On the other hand, by observing the value that can take the flow presented in figure 3, one realizes that:

• 
  if the engine has started, and
  
• if the engine has not taken its step, so that relation (2) becomes:
  
• if the engine has started, and
• if the engine has not started.

This demonstration clearly shows that by integrating the voltage collected at the motor terminals between the instant which is that of the establishment of the pulse and the instant from which the current has substantially ceased in the coil, we obtains two very different voltage levels depending on whether the motor has stepped or not. The above relationships also show that in the proposed detection system the difference in voltage levels is independent of the supply voltage and the internal resistance of the battery.

The operating principle of the detector according to the invention will now be explained in detail by means of the diagram in FIG. 4a.

et que U1 = Um

et que = Rsh · i. Comme Ud = U₁ - U₂ , il en résulte que

A son tour, la tension de sortie g · Ud de l'amplificateur est envoyée à un intégrateur 24 auquel est associée une résistance R et un condensateur C. La tension Uc à la sortie de l'intégrateur s'écrit :

qui en considération de l'équation (2) s'écrit finalement :

Le signal Uc est comparé à une tension de référence Ur dans un comparateur 25. Cette comparaison a lieu 30 ms environ après le début de l'impulsion de commande, grâce à un signal d'horloge provenant du diviseur de fréquence. Si Uc est plus grand que Ur, le moteur a franchi son pas et il n'apparaît aucun signal à la sortie du comparateur : le circuit de commande continue à émettre des impulsions de courte durée. Si au contraire Uc est plus petit que Ur, le moteur n'a pas franchi son pas et il apparaît un signal Us à la sortie du comparateur qui par la ligne 26 oblige le circuit de commande à émettre un train d'impulsions de longue durée 13 comme cela est montré en en figure 2c. Pendant le temps où sont émises les impulsions 13, on bloque l'amplificateur 23 par la ligne 27.The signals from the divider circuit 20 are applied to a circuit 21. This circuit includes the short pulse generator 1, the long pulse generator 6 and the counter 7, as explained in FIG. 1. The output voltage Um has either the shape presented in FIG. 2a, or the shape presented in FIG. 2c depending on whether the motor has taken its step or not. Um is connected to the diagonal ab of a bridge of which one of the branches is occupied by the coil of the motor 22. The voltage Ud which develops on the other diagonal c - d of the bridge is sent to the input of an amplifier gain differential 23. g. It appears from the figure that

and that U1 = Um

and that = Rsh · i. As Ud = U ₁ - U ₂ , it follows that

In turn, the output voltage g · Ud of the amplifier is sent to an integrator 24 with which is associated a resistor R and a capacitor C. The voltage Uc at the output of the integrator is written:

which in consideration of equation (2) is finally written:

The signal Uc is compared with a reference voltage Ur in a comparator 25. This comparison takes place approximately 30 ms after the start of the control pulse, thanks to a clock signal coming from the frequency divider. If Uc is greater than Ur, the motor has passed its pitch and no signal appears at the output of the comparator: the control circuit continues to emit short duration pulses. If on the contrary Uc is smaller than Ur, the motor has not crossed its pitch and a signal Us appears at the output of the comparator which by line 26 obliges the control circuit to emit a train of pulses of long duration 13 as shown in Figure 2c. During the time when the pulses 13 are emitted, the amplifier 23 is blocked by line 27.

FIG. 4b shows an alternative embodiment of the invention. To the motor coil 22 is magnetically coupled a sensing coil 28 at the terminals of which the voltage Ud is developed which, in turn, attacks a circuit similar to that which has just been described.

If we examine equation (3), we see that the parameters which influence the voltage Uc can be classified into two categories: those which depend on the electronic circuit (g, R, C, Rsh, R ₁ and R ₂ ) and that, unique, which depends on the engine and which is the difference in levels of mutual flow at time t = 0 and at time t = T. This last parameter is conditioned by the coupling factor of the motor, by the phase shift between the Torques Cab and Ca and by the existing ratio between the dry friction torque and the Torque Ca. Measurements on models have shown that, taking into account the various circumstances which may arise, the ratio between the voltage Ucminimum produced by a step taken and the maximum voltage Uc existing even if the rotor has not taken its step is greater than 12. It follows from this that the system proposed is very sure since the pitch detection is practically independent of the dispersion of the motor parameters. It also follows that the reference voltage Ur can be chosen within fairly wide limits, which simplifies the construction of the comparator 25.

The short pulse has a duration of about 6 ms and the long pulse a duration of approximately 8 ms. As explained above, the measurement of the voltage Uc by the comparator takes place 30 ms after the start of the control pulse. This value can vary depending on the type of motor used and lower values can be chosen provided that at this point all current has substantially stopped in the coil. We will now understand the reason for the offset between the start of the short pulse and the start of the long pulse train, as shown in Figure 2c. This offset naturally depends on the instant which has been chosen for the measurement of the voltage Uc since the train of long pulses will only intervene, if necessary, after said measurement. The figure shows an offset of 40 ms for a measurement made after 30 ms. If this measurement is made earlier, for example after 15 ms already, the offset can be shortened to 25 ms.

FIG. 5 shows the shape of the voltage Uc and of the current i in the coil when the rotor has crossed its pitch in response to a short pulse of 6 ms and for a well defined type of stepping motor. Curve 1 was noted for a zero torque applied to the motor shaft, curve 2 for a torque of 3. 10-7 Nm and curve 3 for a torque of 6. 10-7 Nm. We see that, if the measurement takes place after a time t> 18 ms, the voltage Uc collected at the output of the integrator has a value of the order of volts. Note here the shift to the right of the current maxima when the torque increases (see publication cited DEOS 27 45 052) but which is not, in the present invention, an operating criterion of the pitch.

FIG. 6 shows the shape of the voltage Uc and of the current i in the coil when the rotor has not taken its step in response to a short pulse of 6 ms. Curve 1 has been recorded for a torque of 9 · 10-7 Nm applied to the motor shaft, curve 2 for a torque of 12 · 10-7 Nm and curve 3 for a torque of 15 · 10-7 Nm. We immediately see that from a time t> 24 ms the voltage Uc at the output of the integrator is very low. Note here that detection of the maximum speed or, if you prefer, a minimum of current between 0 and 6 ms, as proposed in the cited application CH 13 723/72, would conclude with the passage of a step, then that this is not the case as the diagram shows.

As previously mentioned, the main purpose of the system is to reduce the energy consumption of the timepiece and to achieve this by means of an integrator which can be suitable for any stepping motor. If this motor is sized for the servo that the present invention provides, an energy saving of the order of 60% has been measured.

Claims (4)

1. Device for supplying a single-phase stepping motor for a timepiece arranged to control the running of the motor by a first type of bipolar pulses of small width or by a second type of bipolar pulses of greater width , a train of said second type of pulse being sent to the motor if the latter has not progressed by one step in response to said first type of pulse, characterized in that it comprises a step detector comprising first means to collect a first signal Ud developed by the current flowing through the coil of said motor and second means for creating a second signal

the value of which indicates whether the motor has advanced one step in response to a narrow pulse. 2. Device according to claim 1, characterized in that the said first detection means comprise a bridge of which one of the branches is occupied by the motor coil, the first diagonal of the bridge being supplied by the said first or second types of pulses and the second diagonal of the bridge giving the input signal Ud of a differential amplifier whose output is connected to the input of said second means being in the form of an integrator, the output signal Uc of said integrator attacking a comparator which compares said output signal to a reference signal Ur to produce a detection signal Us if the motor has not advanced by one step in response to said narrow pulse. 3. Device according to claim 1, characterized in that said first detection means comprise a pick-up coil inserted into the magnetic circuit of the motor, the voltage developed across said coil constituting the input signal Ud of a differential amplifier the output of which is connected to the input of said second means being in the form of an integrator, the output signal Uc of said integrator attacking a comparator which compares said output signal with a reference signal Ur to produce a detection signal Us if the motor has not progressed by one step in response to said small width pulse. 4. Device according to claims 2 or 3, characterized in that said comparator delivers said detection signal Us as soon as the current has substantially ceased in the motor coil.

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