EP0024737A1 - Detector for the movement of 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 (Ui) developed by the voltage induced in the motor coil (15) during a determined period and for creating a second signal (Us) which is the integral of the first, the amplitude said second signal indicating whether the step has been taken or not. The invention applies to micromotors for timepieces.

Description

The subject of the present invention is a device for supplying a single-phase stepper notor 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.

dont la valeur indique si le moteur a progressé d'un pas en réponse à une impulsion de faible largeur.Control devices of this type are known and, in order to remedy the drawbacks which they present, the applicant has proposed a new solution in her patent application which bears the registration number 8 0 1 0 3 3 6 6. 3 and which claims that the control device 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.

The cited patent application proposes two first possible means for taking the first signal Ud developed by the current flowing through the motor coil.

A detection means comprises a bridge, one of the branches of which is occupied by the motor coil, one of the diagonals being supplied by the driving pulses and the other of the diagonals delivering the signal Ud. If this system has great advantages over those offered by the state of the art, it has the drawback of only taking a very low voltage Ud (of the order of 20 mV) which is a difference between two voltages of large amplitude (of the order of 1 , 5 V). Since the temperature coefficient of the motor coil resistance and that of the other bridge resistances are not the same, it can be shown that the device will not operate safely in a wide temperature range (for example from - 100C to + 600C).

Another detection means proposed by the cited application comprises a sensing coil inserted in the magnetic circuit of the motor, the voltage developed at the terminals of said coil delivering the signal Ud. This signal has the advantage of eliminating the above-mentioned resistance bridge - if the losses it causes and if the coil has a sufficient number of turns the voltage Ud collected will be of a more comfortable amplitude than that arising on the diagonal from the bridge. However, it has the disadvantage of requiring an auxiliary coil in the magnetic circuit of the motor, which increases the construction cost and complicates the wiring of the watch.

It is the _aim of the present invention to eliminate the above drawbacks and to provide a control device which, if it remains based on the general principle described in the cited patent application, offers new means for taking the Ud signal at the motor terminals.

This goal is achieved by the means claimed.

• 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 représente l'allurp du couple mutuel, du couple de positionnement et du flux mutuel aimant bobine en fonction de la position du rotor.
• La figure 4 montre le schéma de principe du détecteur de position selon l'invention.
• La figure 5 est un graphique représentant la tension d'alimentation Ua, la tension induite Ui, la tension Uc à la sortie de l'intégrateur quand le rotor a franchi son pas.
• La figure ₆ est un graphique représentant les mêmes données qu'en fi- ^{gure 5} 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 allurp of the mutual torque, the positioning torque and the mutual flux magnet coil as a function of the position of the rotor.
• Figure 4 shows the block diagram of the position detector according to the invention.
• FIG. 5 is a graph representing the supply voltage Ua, the induced voltage Ui, the voltage Uc at the output of the integrator when the rotor has passed its pitch.
• FIG. ₆ is a graph showing the same data as in ^{FIG. 5} when the rotor has not taken its step.

The invention which will be described ^p aims firstly at reducing the consumption of the timepiece. In fact, 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 sulaliment it, which leads to unnecessary consumption of battery energy. The invention proposes a new device for controlling the pitch of the miller which makes it possible to adapt, with large safety margins, the supply as a function of the load, whence this results in an appreciable gain in energy consumption.

The general principle of supplying the motor as already mentioned in the patent application 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 (for example 6 ms) emitted by the generator 1. A position detector 2, object of the present invention and which will be described in detail below, makes it possible to check whether the motor has its not. 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 device controls, via line 5, the generator 6 which emits long duration pulses (for example 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 period of 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 determined time by the counter, the detector being out of circuit. 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 not succeeded in advancing 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 with respect to the start of the short pulse and when the position detector, after the pulse 12 shown in FIG. 2c; detects an absence of rotation, the long pulse train 13 is sent to the motor during envi- ron 5 minutes, after which the motor is switched again to 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 couples: 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, it will find itself in position S ₂ . In the same FIG. 3, the value of the mutual magnet-coil flux a has been 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.

In the patent application cited above, the applicant proposes to integrate the voltage collected at the terminals of the motor between a time t = 0 and a time t = T pour30 ms for which all current has stopped in the motor coil. This procedure requires the use of the resistance bridge or the auxiliary coil, as explained.

The present invention proposes to use only the main coil of the motor to detect the difference in flux which is equal to the induced voltage developed at the terminals of the coil, integrated between two limits which will be defined below. As this coil is not available during the power supply or driving pulse time, integration can no longer take place from time t = 0, but from time t = t2 which is the time necessary for the motor rotor to take a step, that is to say to pass from position Sl to position S2.

puisque ψ (t2) = ψ (t3) comme cela vient d'être dit. Ceci signifie que si le rotor a franchi son pas, la tension à la sortie de l'intégrateur est substantiellement nulle.As shown in Figure 3, the value of the flow ψ is worth ψ (t2) if the rotor has taken its step and it is in position S2. This value will be the same if it is measured at a time t3 which follows the time t2 and which is distant from it by several milliseconds. Consequently :

since ψ (t2) = ψ (t3) as has just been said. This means that if the rotor has passed its pitch, the voltage at the output of the integrator is substantially zero.

ce qui signifie que si le rotor n'a pas franchi son pas, la tension à la sortie de l'intégrateur est différente de zéro.We will now assume that, following an increase in charge, the rotor has not taken its step. In this case, as shown in Figure 3, the rotor will be at time t = t2, for example at point M located between S1 and S2. At this position corresponds a flux value Y (M). At time t = t3, the rotor will be returned to its starting point Sl for which the value of the flux is ψ (Sl). Consequently

which means that if the rotor has not crossed its pitch, the voltage at the output of the integrator is different from zero.

This demonstration clearly shows that by integrating the induced voltage developed by the motor between a time t = t2 which is that necessary for the displacement of the rotor to its new position S2 and a time t = t3 which follows the time t2 and which is distant from it several milliseconds, two very different voltage levels are obtained depending on whether the motor has stepped or not. For this measurement, it is necessary to put the motor in open circuit between times t2 and t3, which is achieved by a switching circuit which will be explained later. Between the supply period (0 to tl) and the measurement period of the induced voltage (t2 to t3), there is a period of short circuit of the coil (tl to t2) which serves to stabilize the movement of the rotor. Likewise, there is provision between the period t2 to t3 and the moment of the arrival of a new driving pulse in t4 a period t3 to t4 where the motor coil is short-circuited, this allowing the motor to better withstand any shocks that may arise.

Figure 4 shows a possible block diagram for implementing the invention. In this diagram, the coil 15 of the motor receives alternating pulses when the switches 31 - 32, respectively 33 - 34 are closed. These switches form a switching circuit. The table below indicates the position of the switches 31 to 34 according to the periods (0 to tl) to (t3 to t4) defined above and according to the invention. For a positive pulse, the command sequence of the switches is established as follows:

It is quite clear that in the current techniques have been distributed which play the role of switches. In addition, the values of the periods are indicative and suitable for a certain engine construction. Other values could be chosen without departing from the subject of the invention.

est comparée à un signal de référence Ur dans un comparateur 25. Cette comparaison a lieu à la fin de la période d'intégration, c'est-à-dire au temps t3 grâce à un signal d'horloge provenant du diviseur de fréquence. Si Uc est plus petit 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 grand 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 figure 2c. Pendant le temps où sont émises les impulsions 13,on bloque le circuit 22 par la ligne 27.The switching circuit 31 to 34 is controlled by a fitness circuit 21 itself receiving its information from an oscillator-divider circuit 20. This circuit 21 includes the short pulse generator 1 and the long pulse generator 6 and the counter 7, as has been explained with reference to FIG. 1. The control electrodes of the transistors 31 to 34 are controlled by the signals of FIG. 2a according to the sequences of the table above or by the signals of Figure 2c depending on whether the motor rotor has passed its pitch or not. The voltage Ui collected at the terminals of the coil 15 is connected to the input of a differential circuit 22. A control signal 23 opens this circuit during the only period t2 to t3, that is to say during the time when The induced voltage developed by the motor must be read. The voltage Ui collected at the output of circuit 22, made asymmetrical, can attack the integrator 28. At the output of the integrator, the signal

is compared with a reference signal Ur in a comparator 25. This comparison takes place at the end of the integration period, that is to say at time t3 thanks to a clock signal coming from the frequency divider. If Uc is smaller than Ur, the motor has taken its step 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 more large than Ur, the motor has not taken its step and a signal Us appears at the output of the comparator which, via line 26, forces the control circuit to emit a train of long-lasting pulses 13 as is shown in Figure 2c. During the time when the pulses 13 are emitted, the circuit 22 is blocked by the line 27.

As explained above, the measurement of the voltage Uc by the comparator takes place at the end of the integration period, at time t3. As this time t3 is of the order of 30 ms, we will understand the reason for the offset between the start of the short pulse and the start of the train of long pulses, as shown in FIG. 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 depending on the type of motor, for example after 20 ms already, the offset can be shortened to 30 ms.

FIG. 5 is a graph representing the voltage at the terminals of the motor, Ua being the supply voltage, Ui the voltage induced from time t2 and Uc the voltage at the output of the integrator. The graph also shows the current i in the motor coil. In this case, the load applied to the motor is 0.05 _f Nm and it can be seen that the motor has taken its step. The voltage Uc collected at the output of the integrator is zero at time t3 (30 ms), instant of measurement by the comparator, and no signal appears at the output of said comparator.

FIG. 6 is a graph which represents the situation in which the same motor is found for a load of 0.1 _f Nm and for which it is found that the rotor has not taken its step. The voltage Uc collected at the output of the integrator is very large at time t3 (30 ms), instant of measurement by the comparator, and a signal appears at the output of said comparator which forces the control circuit to emit a train d long duration pulses.

The improvements which have just been described give the motor a very safe servo-control, which servo-control has the aim, as already mentioned previously, of reducing the energy consumption of the timepiece and of achieving this by integrating the induced voltage developed in the motor terminals. The system can suit any type of stepper motor. If this motor is sized for the servo offered by the present invention, an energy saving of the order of 60% can be measured.

Claims (1)

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 first means by which, after each bipolar pulse of small width of first period 0 to tl, the motor is put into open circuit during a second period t2 to t3 and second means for detecting a first signal Ui developed at the terminals of the motor during said second period and for creating a second signal

which, if it is greater than a given reference signal, indicates that the motor has not advanced by one step in response to a pulse of small width and that it must be supplied by said train of pulses more large width. 2. Device according to claim 1, characterized in that the motor is short-circuited during a period t1 to t2 located between said first period 0 to tl and said second period t2 to t3 and during a period t3 to t4 located between said second period t2 to t3 and the arrival of the next driving pulse. 3. Device according to claims 1 and 2, characterized in that said first means comprise a control system for controlling the running of the motor by said first type of pulses comprising an oscillator, a frequency divider, a reset circuit form, a switching circuit including the motor coil and that said second means comprise a differential circuit for taking said first signal Ui, an integrator for integrating said signal Ui and creating said second signal Uc and a comparator for comparing said signal Uc 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 1 and 2, characterized in that the value of the times t1 to t3 is included in the following ranges: tl from 2 to 7 ms, t2 from 8 to 20 ms and t3 from 20 to 40 ms.

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