EP0021320B1 - Operation detector for a stepping motor - Google Patents

Description

The present invention relates to a device for supplying a single-phase motor for a timepiece comprising a step detector comprising first means for taking a first signal Ud developed by the current flowing through the motor coil, the device being 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 of greater width, a train of said second type of pulses being sent to the motor if the latter has not increased by one step in response to said first type of pulse.

A control device of this type is known. The German disclosure DE-A-27 45 052 describes a control system which applies to the motor a low energy signal if the motor load is low and a high energy signal if the motor load is high and this for the purpose to reduce the watch's energy consumption by around 60%. 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, during 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 pulses of large width is sent to the motor without any need.

Another control device is described in patent applications FR-A-2,384,289 and FR-A-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 motor with a saturable zone and therefore has the disadvantage of not being applicable to all stepping 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 presented CH-A-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 rotor speed does not necessarily mean that said rotor has taken a step as will appear in the explanations which follow.

US-A-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.

Applications GB-A-2 006 995 and GB-A-2 009 464 also illustrate devices of the same type. In the first request, the induced voltage collected across the motor coil is used in a particular circuit to produce modulated control pulses, while in the second request, a circuit is provided capable of detecting the charging conditions of the motor by means of a high value resistor connected in series with the coil. Neither of these requests calls upon the device which will be described below and which consists in integrating the induced voltage produced by the motor.

It is the object of the invention to eliminate some of the drawbacks presented by the documents mentioned above and to provide a control device which saves energy from 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, les limites d'intégration étant comprises entre l'instant 0 qui est celui de l'établissement de l'impulsion et l'instant T à partir duquel le courant a substantiellement cessé dans la bobine.The supply device according to the invention of the type mentioned above is characterized in that it further comprises second means for creating a second signal

whose value indicates whether the motor has advanced by one step in response to a small width pulse, the integration limits being between instant 0 which is that of the establishment of the pulse and instant T from which the current has substantially ceased in the coil.

• 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 flux 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. It can be seen that a watch micromotor generally works almost 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 flowchart of supply 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 took his step. If so, the decision-maker 3 informs the generator 1 via line 4 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 substitution takes place for a time of n seconds fixed by the counter 7. After this time, the motor is again supplied with 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 for 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 train of long pulses 11 with a duration of the order of 8 ms emitted by 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 from 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 ,. If an impulse is sent to the motor and it takes its step, it will find itself in position S ₂ . In the same FIG. 3, a represents the value of the mutual magnet-coil flux ^p 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=fIux mutuel aimant-bobine.

The differential equation of the voltage collected across a micromotor 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 magnet-coil flux.

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

• Ψ(T)=―(0) si le moteur a fait son pas, et
• Ψ(T)= Ψ(0) si le moteur n'a pas fait son pas,

si bien que la relation (2) devient:

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 the flux present in figure 3 can take, we can see that:

• Ψ (T) = - (0) if the engine has started, and
• Ψ (T) = Ψ (0) if the engine has not started,

so that the relation (2) becomes:

This demonstration clearly shows that by integrating the voltage collected across the motor 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

• 

. 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 Figure 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 motor coil 22. The voltage Ud which develops on the other diagonal cd of the bridge is sent to the input of a differential amplifier 23 gain g. It appears from the figure that

and

• 

• 

As Ud = U ₁ ―U ₂ , it follows that

• 

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

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 larger 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, 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 minimum voltage Uc 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 proposed system is very safe since the detection of the pitch 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 approximately 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 1 at all current has substantially stopped in the coil. We will now understand the reason for the shift 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 taken its step in response to a short pulse of 6 ms and for a well-defined type of stepping motor. Curve 1 has been recorded 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 can 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 1 volt. Note here the shift to the right of the current maxima when the torque increases (see publication cited DE-A-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 was plotted 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 weak. 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-A-13 723 72, would conclude with the passage of a step , while this is not the case as shown in the diagram.

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 dimensioned for the servo offered by the present invention, an energy saving of the order of 60% has been measured.

Claims (4)

1. A feed arrangement for a single phase timepiece stepping motor (22) including a step detector comprising first means arranged to sample a first signal Ud developed by the current through the motor winding, the arrangement being such as to control the functioning of the motor by means of a first type of bipolar pulses of relatively small width (10) or by a second series of bipolar pulses of greater width (11), a series of pulses of the second type being applied to the motor whenever said motor has failed to step in response to pulses of the first type, characterized in that it comprises moreover second means arranged to generate a second signal

the level of which indicates whether or not the motor has stepped in response to a pulse of the first type, the integration limits being taken between the instant (0) when said first type pulse has been established and the instant (T) when current flow in the winding has substantially ceased.

2. A feed arrangement as set forth in claim 1, characterized in that the first means comprise a bridge one branch of which is formed by the motor winding (22), the first diagonal (a, b) thereof being fed by said first or second types of pulses and the second diagonal (c, d) providing the input signal Ud to a differential amplifier (23), the output of which is coupled to the input of said second means which comprise an integrator (24), the output signal Uc of the integrator being sent to a comparator (25) thereby to compare the integrated signal to a reference signal Ur in order to provide a detection signal Us whenever the motor fails to step in response to a pulse of the first type.

3. A feed arrangement as set forth in claim 1, characterized in that the first means include a detection winding (28) in the magnetic circuit of the motor, the potential developed at the terminals of said detection winding constituting the input signal Ud of a differential amplifier (23), the output of which is coupled to the input of said second means which comprise an integrator (24), the output signal Uc of the integrator being sent to a comparator (25) thereby to compare the integrated output signal to a reference signal Ur in order to provide a detection signal Us whenever the motor fails to step in response to a pulse of the first type.

4. A feed arrangement as set forth in claims 2 or 3, characterized in that the comparator (25) provides the detection signal Us as soon as the current in the motor winding has substantially ceased to flow.

Images