EP0135104B1 - Method and device for the control of a stepping motor - Google Patents

Abstract

The method involves supplying to the motor drive pulses generated by a control circuit, determining by means of a measurement circuit a physical magnitude representative of the motion of the rotor, interrupting the drive pulse at a given instant defined by a calculating circuit according to the time taken by the physical magnitude to reach, in a comparator, a reference level, controlling by means of a missed step detecting circuit whether or not the rotor has effected a step, retrieving if need be a non-effected step, summing the number of missed or non-effected steps in a counting circuit, and modifying in a reference circuit the reference level depending on the number of steps that have been missed in a given period of time. The device for putting this method into operation enables the motor to operate under optimal security and energy consumption conditions and can be used to advantage in timepieces.

Description

The present invention relates to a method and a device for controlling a stepping motor and its main purpose is to reduce the consumption of this motor as much as possible while guaranteeing perfect operating safety even in the worst conditions.

The invention finds a particularly interesting application in the field of watchmaking. In fact, in electronic timepieces with analog display which include a stepping motor to drive the display members, most of the energy supplied by the electric power source, which is in generally a battery, is consumed by the engine. It is therefore important to limit, as much as possible the consumption of this motor to increase the life of the battery or, for a given life, to be able to reduce its volume, the space available in a timepiece being very limited. .

In most timepieces currently on the market, the duration of the driving pulses sent at regular intervals to the motor is fixed. This duration, generally 7.8 ms, is provided in order to guarantee the proper functioning of the motor even under the worst conditions, that is to say with a low battery voltage, during the drive of the calendar mechanism , in the presence of shocks or external magnetic field, etc. As these unfavorable conditions occur only rarely, the engine is mostly supercharged.

A known solution for reducing the power consumption of the motor consists in applying normal motor pulses of reduced duration, for example 3.9 ms, but sufficient to ensure correct operation under the best conditions and to provide a device which, after each of these pulses detects whether or not the motor has run. In the absence of rotation, this detection device controls the sending to the motor of a long-term catching pulse, which allows the latter to take the missed step. Although it undoubtedly constitutes an improvement on the case where the motor is powered only by long-lasting pulses, such a system is not satisfactory because, in the case where the motor does not run in response to a normal pulse, its energy is completely lost and very often the duration of the catch-up pulse is much greater than that necessary for the motor to take its step.

Other systems use means for detecting changes in the engine load and for switching the duration or amplitude of the driving pulses to a higher value when an increase in the load is detected. Such systems, like the previous one, are in fact only safety devices which simply make it possible to deliver to the engine an additional energy, often overabundant when necessary.

In fact, it is only possible to significantly reduce the energy consumption of the motor by associating it with more advanced control devices which make it possible to adapt the energy of the driving pulses to the momentary load which it must drive and to the supply voltage.

It has been proposed in particular to provide a pulse forming circuit capable of producing pulses of several different durations associated with a device which, as before, detects the rotation or the absence of rotation of the motor and gradually reduce the duration of the pulses. sent to the motor until a step not taken is detected. A catch-up pulse of maximum duration is then applied to the motor and the energy of the normal driving pulses is fixed at the nearest higher value. If the next step is not carried out, a new increment is carried out. Otherwise the value is maintained for a certain time. If the engine has been running normally during this period, the pulse duration is further reduced. Such a solution does not allow permanent and rapid adaptation of the driving pulses to the load of the motor; this adaptation is only carried out on average. Furthermore, as in the case of the first system mentioned above, the sending of catch-up pulses in the event of non-rotation means that the energy consumption is higher than necessary.

There are systems which effectively allow the energy of the driving pulses to be permanently controlled by the motor load and the battery voltage. These devices include means for measuring, during the application of the driving pulse, an operating parameter representative of the position or the speed of the rotor and for interrupting this pulse at an instant determined as a function of the time taken by the physical quantity. measured to reach a predetermined reference level, corresponding to the moment when the rotor has taken its step or, at least, has turned by an amount or acquired a speed sufficient to complete this step. Such a system is undoubtedly the most effective. However, in practice, in order to fix the reference level, it is necessary to take account of the dispersions and variations in the characteristics which may exist for the motor and for certain components of the control circuit which is associated with it. The value chosen is therefore not that which corresponds to minimum consumption.

The present invention also aims to eliminate this drawback.

This object is achieved thanks to the fact that the method according to the invention for controlling a stepping motor comprising a rotor and a coil receiving normal driving pulses from a control device associated with the motor to rotate the rotor when this device is energized, does not only consist in measuring, during each normal driving pulse, a physical quantity representative of the movement of the rotor and in interrupting said driving pulse at an instant determined as a function of the time taken by the physical quantity measured to reach a reference level, but also to detect the condition of rotation or non-rotation of the rotor in response to normal driving pulses and to modify the reference level by based on the information provided by this detection.

Thanks to this it is possible to adapt the reference level to the specific characteristics of each motor and to that of the control device associated with it, so as to have an optimal performance of the assembly, this while maintaining a very high operating safety for the engine.

According to a particular form of the method according to the invention, the reference level is adjustable in steps between a minimum value and a maximum value and it is increased by one step when N steps not taken by the rotor in response to normal driving pulses have have been detected in a determined time interval, N being a number which may be equal to or greater than 1.

Advantageously, the steps not taken by the rotor in response to normal driving pulses are caught up by applying to the motor coil correction driving pulses of sufficient duration to ensure the rotation of the rotor.

The control device which makes it possible to implement the method according to the invention comprises means generating signals producing an output signal each time the rotor must take a step, control means for applying normal driving pulses to the coil of the motor in response to the output signals supplied by the signal generating means, means coupled to the motor for measuring during each normal driving pulse the physical quantity characteristic of the movement of the rotor and supplying a measurement signal representative of this quantity, means for producing a reference signal corresponding to the reference level, means for providing a comparison signal between the measurement signal and said reference signal, means which receive the comparison signal and which act on the control means to interrupt the normal driving impulse at an instant determined as a function of the time taken by the physical quantity to reach n reference level, as well as detection means for detecting the condition of rotation or non-rotation of the rotor, the means which produce the reference signal being designed to be able to modify the value of this signal as a function of the information provided by the means of detection.

• la fig. 1 est un schéma bloc d'un exemple de dispositif de commande selon l'invention dans lequel le paramètre choisi pour l'asservissement de la durée des impulsions motrices à la charge du moteur est la tension induite dans la bobine de ce moteur par le mouvement du rotor;
• la fig. 2 représente la tension délivrée par un circuit de mesure de la tension induite faisant partie du circuit de la fig. 1 lorsque le moteur tourne normalement, lorsque le rotor est bloqué et que l'impulsion motrice est en phase et enfin lorsque l'impulsion motrice est en contrephase;
• la fig. 3 est un schéma d'un circuit de détection des pas ratés pouvant être utilisé dans le dispositif de commande selon l'invention;
• la fig. 4 montre la forme des principaux signaux apparaissant dans le circuit de la fig. 3;
• la fig. 5 est un schéma d'une forme possible de réalisation du circuit de commande du moteur pas-à-pas représenté sur le schéma-bloc de la fig.1;
• la fig. 6 montre la forme des principaux signaux apparaissant dans le circuit de la fig. 5;
• les fig. 7 et 8 sont des schémas respectivement d'un compteur de pas ratés et d'un circuit fournissant une tension de seuil variable U' qui peuvent être utilisés dans le dispositif de l'invention; enfin
• la fig. 9 montre la forme des principaux signaux apparaissant dans les schémas des fig. 7 et 8, en particulier l'évolution de la tension de seuil U_s en fonction du temps et des pas ratés.

Other characteristics and advantages will emerge from the description which follows, given with reference to the appended drawings and giving, by way of explanation but in no way limiting, an example of implementation of the present invention. In these drawings:

• fig. 1 is a block diagram of an example of a control device according to the invention in which the parameter chosen for controlling the duration of the driving pulses at the load of the motor is the voltage induced in the coil of this motor by the movement rotor;
• fig. 2 represents the voltage delivered by a circuit for measuring the induced voltage forming part of the circuit of FIG. 1 when the engine is running normally, when the rotor is locked and the driving pulse is in phase and finally when the driving pulse is in reverse;
• fig. 3 is a diagram of a missed step detection circuit that can be used in the control device according to the invention;
• fig. 4 shows the form of the main signals appearing in the circuit of FIG. 3;
• fig. 5 is a diagram of a possible embodiment of the control circuit of the stepping motor shown in the block diagram of FIG. 1;
• fig. 6 shows the form of the main signals appearing in the circuit of FIG. 5;
• fig. 7 and 8 are diagrams respectively of a missed step counter and of a circuit providing a variable threshold voltage U ′ which can be used in the device of the invention; finally
• fig. 9 shows the form of the main signals appearing in the diagrams of FIGS. 7 and 8, in particular the evolution of the threshold voltage U _s as a function of time and missed steps.

A stepper motor control system where the voltage induced in the motor coil by the movement of the rotor is measured and compared to a threshold or reference level to allow adaptation of the duration of the driving pulses to the instantaneous load of the engine has already been the subject of the European patent application filed on January 21, 1982 in the name of Asulab SA and published under the number 60806. Naturally, as in other known systems of the same kind where the other parameters than the induced voltage are used to control the interruption of the driving pulses, the threshold level is fixed. This does not prevent certain elements of the device described in this European application from being found as such or in a slightly modified form in the embodiment which has been chosen by way of example to demonstrate the invention.

Reference will therefore frequently be made thereafter to this earlier European application, whether for the purpose of making comparisons or not having to describe again in detail the circuits or parts of circuits which have already been described in the document in question.

To avoid confusion, the elements of the known device which are found in that of the invention are designated by the same references in the present application as in the aforementioned European application. For example, the circuit for calculating the induced voltage which bears the reference 11 in FIG. 4 of the European patent application is designated by the same number in FIG. 1 of this application. It is the same for the circuit for calculating the duration of the driving pulses 13. Note that the same rule also applies to the signals which are the same in both cases.

On the other hand, the elements which fulfill the same function in the device of the invention as in the known device but which had to be modified carry in the present application a reference which is increased by 100 compared to the corresponding reference used in the application anterior. For example, the AND gate 43 with two inputs which drives the motor control transistors of FIG. 12 of the European demand becomes, in fig. 5 of the present application, the AND gate 143 with 3 inputs, these two doors fulfilling basically the same role.

Finally, any element which appears only in the present application bears a reference equal to or greater than 200.

The control device according to the invention which will now be described and the general diagram of which is shown in FIG. 1, which is to be put in parallel with FIG. 4 of the aforementioned European patent application, is intended to equip an electronic watch with second hand.

This device comprises a periodic signal generator circuit 8 constituted by a quartz oscillator 300 which produces a signal whose frequency is substantially equal to 32768 Hz and by a frequency divider 400 which, after a division by fifteen binary stages of the frequency of the oscillator and a shaping of the wave, delivers at its output which also constitutes that of circuit 8 a signal S ₈ of 1 Hz, formed of fine pulses whose duration is, for example, equal to the period of the signal of the oscillator, about 30 µs.

A combinational logic circuit 203 is connected to the various outputs of the binary stages of the frequency divider 400 by a series of connections to produce three logic signals SA, SB, SC, which are necessary for the operation of the device and whose form will be specified later. This circuit 203 which also has the function of dividing the output signal of the last binary stage of the frequency divider and of providing periodically, for example every hour, a fourth signal SD whose usefulness will also appear later, can be produced in a simple way that is within the reach of the skilled person. It will therefore not be described in detail here.

A control circuit 109, fulfilling a role similar to circuit 9 of the cited European application, has a first input connected to the output of the frequency divider 400, which supplies the signal S ₈ . The output of circuit 109 delivers driving pulses I to a stepping motor 10. A second input of circuit 109 receives a signal S ₁₃ for stopping the driving pulse I, as described in the cited reference. Finally, in accordance with the present invention, a third input of circuit 109 receives a signal Q211 to make up for missed steps. A resistor 18, visible in FIG. 5, connected in series with the motor 10, makes it possible to obtain at its terminals a voltage U19 representative of the current which flows through the motor during the driving pulse I.

A computing circuit 11, represented by FIG. 11 in the European reference cited, receives on its input the signal U19 and develops a measurement voltage U _m , representative of the voltage induced by the rotor during its rotation, which appears at the output of this circuit, across the resistor 82 of European demand.

A comparator circuit 12 has a first input connected to the output of circuit 11 while a second input receives a reference or threshold voltage U ' _S. This comparator 12 delivers at its output a logic signal S12 which is at the low logic level if U _m is less than U ' _s and at the high logic level if U _m is more than U' _s . The threshold voltage U ' _s is chosen as a function of the amplitude of the measurement voltage U _m obtained under these normal engine operating conditions, as will appear below. The moment of transition of the signal S ₁₂ from the low logic level to the high logic level, counted from the start of the driving pulse I, defines a time T ₂ which is representative of the torque C supplied by the motor.

The output of comparator 12 is connected to a first input of a calculation circuit 13, which determines the duration of the driving pulse I, and the output of the frequency divider 400 is connected to a second input of this circuit. At the output of circuit 13, the logic signal S ₁₃ appears. This signal is generated by the circuit 13 from the signals S ₈ and S ₁₂ and it is applied to the second input of the control circuit 109. The signal S _i3 is normally at the low logic level and goes to the high logic level T ₃ seconds after the transition of signal S ₁₂ . A high logic level of the signal S ₁₃ has the effect of stopping the driving pulse 1 produced by the control circuit 109. The duration T _l of the driving pulse therefore takes account of the torque C which the motor must supply and it is worth T ₁ = T ₂ + T ₃ .

The output of circuit 11, on which the measurement voltage U _m appears, is connected to the input of a missed step detector circuit 200. The output of circuit 200 is connected to the third input of circuit 109 and to the input of a missed step counting circuit 201. On the output of circuit 200 a logic signal Q211 appears which is normally in the logic low state and goes to the logic high state for one second, for example, after detection with a failed step. The output of the counting circuit 201 is connected to a first input of a voltage reference circuit 202. The output of this latter circuit, supplying the threshold voltage U ' _s , is connected to the second input of the circuit 12. The signal S220 appearing at the output of circuit 201 is formed by pulses. A pulse is generated as soon as the circuit 201 has counted N not missed in Tn seconds. Typically N = 5 and Tn = 8s.

At each pulse of the signal S220, the circuit 202 increments the threshold voltage U ' _s by a fixed step. The voltage U ' _s can thus vary between a minimum level U' _so , which can be equal to 0, and a maximum level U ' _sp in P steps. P is for example 10. Once U ' _s has reached its maximum level, it remains there even if circuit 202 receives other impulses. Circuit 202 has a second input to which a signal S226 is applied. This signal reduces the voltage U ' _s to the minimum value U' _so each time that the entire circuit of FIG. 1 is switched on, for example when the battery is changed. Finally, the voltage U ' _s is again periodically reduced to U' _so , for example every hour, by the signal SD produced by the combinational logic circuit 203 and applied to a third input of the circuit 202.

To explain the operation of the device in fig. 1, it is advantageous to break it down into two loops. By excluding circuits 8 and 203 placed outside these loops, the first, or the bottom one, includes the elements referenced 109, 10, 11, 12 and 13. The second loop, or the top loop, includes the elements 109, 10, 11 and 200 with, in addition, a branch formed of the elements 201 and 202.

If we ignore the catching up of missed steps and assume that the threshold voltage U ' _s remains constant, the bottom loop returns to the diagram in fig. 4 of the cited European application, the circuit 109 then being replaced by the circuit 9. In this request is found the detailed description of the elements and circuits 9, 10, 11, 12 and 13 as well as the explanation of the operation of the assembly of the device. It should be recalled that this device makes it possible to optimally adapt the duration T _l of the driving pulse I to the torque C which the motor must supply by measuring the time T ₂ which takes the measurement voltage U _m to reach the threshold voltage U ' _s . This optimal operation, corresponding to a minimum consumption of the engine, is however only achieved if the characteristics k and K of the engine are equal to those introduced into the calculation circuit 13 which determines, from time T ₂ , a time T ₃ which, added to T ₂ , gives the duration T ₁ of the driving impulse I.

However, as has already been indicated, in production, the characteristics of the motor, of circuit 13 and of the other circuits of the bottom loop inevitably have a certain dispersion. As a result, the condition of minimum consumption of the engine is rarely achieved in practice, even less if the engine is replaced by another model with different characteristics. This naturally represents a serious limitation in the use of this control device.

The upper loop for catching up on lost steps, in connection with the branch formed by circuits 201 and 202 which controls the threshold voltage U ' _s , makes it possible to largely overcome the need to match the constants of circuit 13 to the constants k, K of the motor and to make the device less sensitive to variations in the parameters of the other circuits.

Indeed, the failed step counting circuit 201 makes it possible to define a satisfactory operating criterion of the motor when it is subjected to external disturbances. One can estimate for example that if the motor, following angular shocks or an intense magnetic field, does not lose more than 4 steps per period of 8 seconds, the energy of the driving impulses I is sufficient. No pulse will be produced by the circuit 201 and the threshold voltage U ' _{s will} continue to keep its value. If, on the other hand, the number of steps lost per period of 8 seconds exceeds 4, the energy of the motor pulses will be considered as insufficient. One or more pulses will then be generated by the circuit 201 in which the constants N = 5 and Tn = 8 seconds have been introduced. Each pulse on the signal S220 produces the incrementation of a step of the threshold voltage U ' _s of the circuit 202. Now, all other things being equal, at a higher voltage U' _s corresponds an energy of the driving pulse 1 plus big. This adaptation process can continue until the energy of the motor impulses satisfies the satisfactory operating criterion adopted. All the steps missed during this adjustment process are naturally caught up. To take account of the evolution of the characteristics of the motor over time, at each change of battery, or periodically, for example once per hour, the voltage U ' _s is reset to the minimum value U' _so using S226 or SD signals. The value U ' _s obtained after the readjustment process then corresponds to the new engine operating conditions.

Let us now examine how the circuit 11 reacts to a driving pulse 1 applied to the motor 10 in various situations. In our example the motor is of the stepping type and the driving pulses 1 are polarized. This means that to turn the motor one step from a given position, the driving pulse 1 must have the correct polarity with respect to the position of the rotor or, as we say, be in phase with the latter. Otherwise, if the pulse I has the wrong polarity, that is to say that it is in counterphase with the position of the rotor, the motor will not run.

Three cases are to be considered and for each the measurement voltage U _m supplied by the circuit 11 of the present invention, corresponding to the circuit of - FIG. 11 of the cited European reference, is represented by a curve in FIG. 2. The first corresponds to the normal case, that where the motor 10 receives a driving pulse 1 in phase and takes a step. The measurement voltage U _m represented by curve 205 in FIG. 2 is then a faithful image of the voltage induced by the rotation of the motor. This curve is characterized by a strong positive point. The second case is that where the motor 10 receives a pulse I in phase but does not rotate, its rotor being blocked. The induced rotation voltage is then zero while the measurement voltage U _m produced by the circuit 11 in this situation, represented by the curve 206, shows a low amplitude oscillation. Finally, in the third case, the motor receives a pulse 1 in counterphase. It cannot then rotate and the induced voltage is therefore also zero. On the other hand, the measurement voltage U _m takes a strong negative value, as the curve shows. 207 corresponding to this case in fig. 2. This stems from the fact that the magnetic flux created by the magnet of the rotor and that produced by the pulse 1 are added and saturate certain parts of the stator. This saturation has the effect of modifying the time constant UR of the motor, L being its inductance and R the resistance of the coil. However, this time constant is used in circuit 11 to determine U _m . Thus in the case where the driving pulse I is in counterphase, the circuit 11 supplies a measurement voltage U _{m which is} erroneous but easy to detect. It suffices, in fact, to compare it with a negative reference voltage U _R. If the resulting voltage is positive, the motor has run, if it is negative the motor has missed a step.

From the above, it can be seen that if the motor misses a step by blocking the rotor, the next driving impulse I, coming in counterphase, will allow the lost step to be easily detected. As the driving impulse I in counterphase is incapable of turning the motor, there will be a total of two lost steps.

Fig. 3 shows the constitution of the missed step detection circuit 200. This circuit includes a differential amplifier 210 whose output is connected to the terminal S for setting a bistable flip-flop 211. The non-inverting input of the amplifier 210 is connected to a voltage reference not shown, supplying the negative voltage U _R. The inverting input of the same amplifier constitutes the input of circuit 200. This input is connected to the output of circuit 11 to receive the measurement voltage U _m . The flip-flop 211 has a reset input R which is connected to the output of the frequency divider 400 to receive the signal S ₃ . Finally, the output terminal Q of the flip-flop 211 also constitutes the output of the circuit 200.

The operation of the circuit of fig. 3 will now be described with the help of the signals shown in FIG. 4 which appear at the different points of this circuit. The signal Sε comes from the output of the frequency divider 400 and it includes fine seconds pulses. The duration of these pulses is equal to the period of the signal of 32768 Hz coming from the quartz oscillator 300. The voltage U _m is formed, in synchronism with the signal S ₈ , of positive pulses when the driving pulse 1 is in phase with the position of the motor rotor, whether it rotates or not, and negative pulses when pulse 1 is in counterphase. The comparison of the voltage U _m with the negative reference voltage U _R in the differential amplifier 210 produces at its output a signal S210. If the gain of the amplifier 210 is sufficiently high, the signal S210 will be at the low logic level when U _m is greater than U _R and at the high logic level during the time when U _m is less than U _R. The signal S210 therefore contains a positive pulse of a few milliseconds, slightly behind the pulses of the signal S ₈ , when a missed engine step is detected.

The flip-flop 211 receives on its inputs R and S respectively the signals S ₈ and S210. The signal Sa resets the flip-flop to zero every second, which causes a low logic level on its output Q. At each positive pulse of the signal S210 the flip-flop is set to the state, causing a high logic level on the output Q until the next pulse of the signal S ₈ . The logic signal Q211 which appears on the output Q of the flip-flop 211 is thus normally at the low logic level. It goes to the high logic level after the detection of a missed step and goes back to the low level a second later.

The instants corresponding to the different situations of the engine which have just been described, are noted on the time scale t of FIG. 4. At the instant TA the motor receives a driving pulse I in phase and it rotates normally. The rotor of the motor is supposed to be locked at time TB when the driving pulse in phase produces a voltage U _m of lower amplitude than previously. The next driving pulse 1 then comes in counterphase at time TC, the motor cannot turn, whether the rotor is free or blocked, and the voltage U _m produced is negative. This causes the Q211 signal to go to high logic state. About half a second later, at the instant TD, while the signal Q211 is still at the high logic level, the motor receives, by means which will be described later, two driving pulses of recovery producing the two positive pulses close to the measurement voltage U _m . The watch then caught up with the two lost steps. Finally, still half a second later, at time TE, the motor receives a driving pulse I in phase and turns normally.

Fig. 5 of the present invention is to be compared with FIG. 12 of the previous European application. In these two figures, the blocks 11, 12 and 13 already mentioned are distinguished. Block 9 of fig. 12 is however replaced by block 109 in FIG. 5. Block 109 shows the composition of the motor control circuit 10 according to the present invention. This block has the same general structure as block 9, despite some modifications and the presence of additional elements.

These modifications have two purposes. First of all, they make it possible to cut off, after a determined time, the driving pulse 1 in the absence of the stop signal S ₁₃ = S57 of this pulse. This can happen if the measurement voltage U _m is insufficient to trigger the signal S13 following, for example, the blocking of the motor 10. Second, these modifications make it possible to introduce two catch-up driving pulses between two normal motor impulses, when a missed step has been detected. In these two possibilities, the duration of the driving pulses is fixed and corresponds to the optimal duration, that is to say that which allows the motor to transmit the maximum torque. In the case of a stepping motor for a watch, the optimal duration is typically 7.8 ms, equal to the period of a signal of 128 Hz. It is to this value that reference will be made thereafter.

The circuit represented by block 109 of FIG. 5 of the present invention comprises the elements 10, 14, 15, 16, 17, 42, 45 and 58 already described in the cited European document, the gates ET 143 and ET 144 which have one more entry than the gates ET 43 and ET 44 of the cited document and finally a door AND 215 and three doors OR 216, OR 217 and OR 218 additional.

The output of the frequency divider 400 is connected to the first input of the OR gate 216 of FIG. 5. This input thus receives the second signal Sε. The output of the missed step detection circuit 200 is connected to the first input of the gate with two AND inputs 215, which thus receives the signal Q211. The output of the AND gate 215 is connected to the second input of the OR gate 216. The output of the latter gate is connected to the clock input C _K of the flip-flop 42, to the input of the AND gate 58 operating as an inverter and finally at the clock input C _K of the flip-flop 46, the latter being part of block 13. The first input of the OR gate 217 is connected to the terminal of the combinational logic circuit 203 which produces the logic signal HER. The second inputs of the doors with two AND inputs 215 and OR 218 are connected together and the common point is connected to the output of the logic circuit 203 which generates the logic signal SB. The second input of the OR gate 217 is connected to the output of the AND gate 215 and the first input of the OR gate 218 is connected to the output Q of the flip-flop 45. The output of the OR gate 218 is connected to the second inputs doors with three inputs AND 143 and AND 144. The third inputs of these same doors AND 143 and AND 144 are connected to the output of the OR gate 217. The first input of the AND gate 143 is connected to the output Q of the flip-flop 42 and the first input of AND gate 144 at the output Q ^* of the same flip-flop. Finally the outputs of the doors ET 143 and ET 144 are connected to the control transistors 14, 16, 16, 17 of the motor 10 and the terminals Q ^* and R of the rocker 45 respectively to the elements 51 and 57 of the block 13, as is described in the cited European document.

Before describing the operation of the circuit in fig. 5, let's examine the signals shown in fig. 6 that this circuit receives. The signal S ₈ , already described in the cited reference, is composed of positive seconds pulses with a duration of around 30 µs. The signal SA is also composed of seconds pulses, synchronous with the pulses of the signal S ₈ , but their duration is 7.8 ms. The signal SB is formed by a series of pairs of pulses. Each pulse of the signal SB has a duration of 7.8 ms and each pair of pulses is located between two successive pulses of the signal S ₈ . In the example of fig. 6, the pulses of the signal SB forming a pair are separated by an interval of 7.8 ms and each pair of pulses is located in the middle of the interval formed by two successive pulses of the signal S ₈ . signal Q45 has been described in the European reference cited when the engine is running normally. This signal is then formed of positive pulses, the duration of which determines that of the driving pulses I and varies as a function of the motor torque supplied. When the motor is blocked and loses a step, the amplitude of the measurement signal U _m is insufficient to reach the threshold voltage U 'and produce the signal S13 to reset the flip-flop 45 to zero. The signal Q45 then remains at the level logic high until the next catch-up motor pulse whose fixed duration of 7.8 ms is assumed to be sufficient to run the motor in the most unfavorable cases. The signal 0211 has already been described with reference to FIGS. 3 and 4. This signal goes to the high logic level after detection of a missed step and remains in this state until the next pulse of the signal S ₈ . The signals S143 and S144 represent the driving pulses of the control transistors 14, 15, 16, 17 of the motor 10 in the case of normal operation and in that of the recovery of the lost steps. With the exception of the catch-up pulse pairs, the start of all the other pulses are synchronous with the start of the pulses of signal S ₈ . Finally the time scale t indicates, as in fig. 4, in TA a normal rotation of the motor, in TB a missed step, in TC the detection of a missed step, in TD 1 and TD 2 the two catch-up steps and in TE again a normal rotation step.

The operation of circuit 5 and in particular of block 109 will now be described with the help of the signals shown in FIG. 6. When the engine is operating normally, signal Q211 is at low logic level since there have been no missed steps. The output of the AND gate 215 then also remains at the low logic level, whatever the level of the signal SB. The OR gate 216 then transmits, without modifying it, the signal S ₈ which is thus applied to the terminals C _K of the flip-flops 42 and 46 and to the input of the gate 58.

The output of the OR gate 217 provides a signal formed by the signal SA in normal operation and by the superposition of the signals SA and SB just after the detection of a missed step. Similarly, the output of the OR gate 218 provides a signal formed by the superposition of the signals SB and Q45. The normal driving pulses 1 coming in synchronism with the signal S ₈ , appear while the signal SB is at the low logic level. The signal SB therefore has, in this case, no effect on the OR gate 218 which then transmits only the signal Q45 defining the duration of the driving pulse I. Thus at the time of a normal driving pulse 1, the signal at the output of the OR gate 217 is at the high logic level for 7.8 ms and the signal at the output of the OR gate 218 at the logic level also high, but for the duration of the pulse of the signal Q45. When the engine load is normal, the duration of the Q45 signal pulse is approximately 4 ms, much less than the 7.8 ms duration of the SA signal pulse. These signals being applied to the gates AND 143 and AND 144, we find the pulse of the signal Q45 at the output of the first gate if the output 0 of the flip-flop 42 is at the high logic level, and at the output of the second gate if it is the exit Q ^* of the same rocker which is in this state. As a result, the signal S143, which is at the output of the AND gate 143, has a period of two seconds and that it is formed of pulses which are inserted in the middle of the distance separating two successive pulses from the similar signal S144 supplied by the AND gate 144. The signals S143 and S144 drive the control transistors 14 to 17, which generate the driving pulse I.

Thus, when the engine works under normal conditions, the block 109 of FIG. 5 of the present invention operates identically to block 9 of FIG. 12 of the European reference cited. This situation corresponds to the instant TA of the time scale t of FIG. 6.

Let us now examine the case where the motor does not turn, in response to a driving pulse I in phase, and therefore loses one step. This corresponds to the instant TB of the time scale t of FIG. 6. Under these circumstances, the measurement voltage U _m remains lower than the threshold voltage U ' _s , as already explained. The signal S12 produced by block 12 then remains at the low logic level. The block 13, not receiving a control pulse from the block 12, cannot in turn generate the signal S13 which would stop the driving pulse by passing the signal Q45 from the high logic state to the low logic state. Thus, the engine being blocked, the driving pulse 1 once triggered would be maintained indefinitely in the case of block 9 of the European reference cited. On the other hand, with the block 109 of the present invention, even if the signal Q45 remains permanently at the high logic level, the driving pulse cannot last longer than the 7.8 ms of the pulse of the signal SA. Indeed, the signal SA, passing through the OR gate 217, controls the AND gates 143 and AND 144 by allowing the passage of the signals applied to the inputs of these gates only during the time when the signal SA is in the high logic state.

The engine having missed a step, the following driving impulse 1 comes in counterphase and it is in principle incapable of turning the engine. This corresponds to the instant EC of the time scale t of FIG. 6. The circuit 200 makes it possible at this instant to detect the non-rotation of the motor during the previous driving pulse by passing the output signal Q211 from the low logic state to the high logic state. The signal Q211 remains in this state until the next pulse of the signal Sa at the instant TE of the time scale t of FIG. 6, thus defining a window with a duration of 1 second.

Just after the moment TC shown in fig. 6, the motor has thus lost two steps which must be caught up before time TE, for example in the middle of the time interval separating TC from TL, at the instants TD1 and TD2 defined by the corresponding pair of pulses of the signal SB . The signal Q211 is then at the high logic level, which allows the two pulses of the signal SB to pass through the AND gates 215 and OR 216 to reach the terminal C _K of the flip-flop 42 of FIG. 5. The signal SB then also passes through the OR gate 217, to reach the third inputs of the AND gates 143 and AND 144. The first pulse of the signal SB puts the flip-flop 42 in a state making it possible to produce a driving pulse in phase with the instant TD1, since the driving impulse at the instant TC was in counterphase and the engine had not turned. In the case shown in fig. 6, it is the output Q ^* of the flip-flop 42 which must pass to the high logic level. As the signal SA is at the low logic level in the vicinity of the instants TD1 and TD2, at the output of the OR gate 218 there are only the two pulses of the signal SB. On the other hand, at time TD1 the logic level of the output signal from the OR gate 218 is in the high logic state because the logic signals SB and Q45 are also in this state. It follows that at time TD1 the signal S143 is at the low logic level and the signal S144 at the high logic level. A driving pulse I in phase is then produced by the control transistors 14 to 17. The rotation of the motor brings the signal Q45 to the logic low level approximately 4 ms after the start of the driving pulse as in the normal case. This transition of the signal Q45 does not however stop the driving pulse I in the case of catching up with a lost step. Indeed, at the output of the OR gates 217 and OR 218, the two pulses of the signal SB are then found, which determine the duration of the driving pulses, equal to 7.8 ms. At the instant TE, after having caught the two lost steps, the motor works again normally.

Let us now consider the missed step counting circuit 201, represented in FIG. 7. It essentially comprises a counter by N referenced 220. The value of N is typically equal to 5. This counter has an input terminal, an output terminal and a reset terminal R.

The input terminal receives the signal Q211 coming from the missed step detector 200. The output terminal delivers a signal S220 formed by a pulse of arbitrary duration, each time the counter has counted by N. Finally, the terminal R receives a reset signal SC taken at the output of circuit 203 whose period T _n is, for example, 8 seconds. Thus if there are 5 or more missed steps in an 8 second period, the output signal S220 will include a pulse at the end of this period. The pulses of signal S220, designated by A, B, ... P in fig. 9, are naturally distributed irregularly over time. All the missed steps are of course made up.

Finally, let us examine the voltage reference circuit 202, shown in FIG. 8. This circuit includes a counter by P, referenced 221, having an input terminal, a reset terminal S and p output terminals denoted a, bc .. p. The value of P is typically equal to 10. The input terminal receives the signal S220, coming from the missed step counting circuit 201, and the reset terminal S is connected to the output of an OR gate 225 with two entrances. The first input of this gate receives the signal SD, supplied by the circuit 203, which gives, for example, a pulse every hour. The second input is connected to a circuit 226, not described but known per se, which delivers an output signal S226 containing a pulse when the battery which supplies the supply voltage U _a is placed in the watch. The output terminals a, b, ... p of counter 221 are each connected to the control terminal of a transmission door, the transmission doors being denoted respectively 223a, 223b, ... 223p. Each transmission door connects the first terminal of a first load resistor 224, common to all these doors, to the first terminal of a second load resistor. Each transmission gate therefore corresponds to a second load resistance and these p resistors are denoted respectively 224a, 224b, ... 224p. The second terminals of resistors 224, 224a, 224b, ... 224p are all connected to ground. A transmission door is made conductive when its control terminal is brought to the high logic level. If not it is in the blocking state. Between the supply terminal Ua, connected to the watch battery, and the first terminal of the resistor 224 is connected a current source 222. This source delivers a constant current IR. Finally, the threshold voltage U ' _s constituting the output of circuit 202, is taken from the first terminal of resistor 224.

The operation of the circuit of fig. 8 will now be described with reference to the signals shown in FIG. 9. This last figure represents the variations of the signals S221 a, S221b, ... S221 p, appearing on the output terminals a, b, ... p of the counter 221, as a function of the pulses A, B, ... P contained in the signal S220, as well as the variations in the threshold voltage U ′ which result therefrom. At the initial instant the counter 221 is reset by a pulse of the signal S220 or of the signal SD, this pulse being transmitted to the terminal S of the counter by the OR gate 225. The signals S221 a, S221 b ,. .. S221 p are then all at the high logical level. The transmission doors 223a, 223b, ... 223p, controlled by these signals, are thus all made conductive. It follows that the load resistors 224a, 224b, ... 224p all come in parallel on the load resistor 224. The paralleling of all these resistors defines a minimum equivalent load resistance. The current source 222 delivering a constant current IR in this equivalent load resistance, produces at its terminals a minimum threshold voltage U ' _so . If the energy of the driving pulse I corresponding to this threshold is insufficient for the motor to function satisfactorily within the meaning of the criterion stated above, a pulse A will be generated by the circuit 201 and transmitted by the signal S220 to the counter 211 , which will advance by one. In this new state of the counter, the output signal S221a goes to the low logic level, the other outputs remaining at the high logic level. The transmission door 223a then passes from the conducting state to the blocking state and disconnects the resistor 224a from the resistor 224. The equivalent load resistance therefore increases in value. It is the same for the threshold voltage which goes from U ' _so to the directly higher value U' _sa . The same process can be repeated, if necessary, with the pulses B, C, ... P incrementing, each time, the threshold voltage by one step up to the maximum value U ' _s p. With the P + 1 pulse, the threshold voltage drops to the minimum value U ' _so and the cycle can start again. In practice, the threshold voltage must stabilize at a value below U ' _sp , the return to the minimum value U' _so being produced only by the pulses of signals S226 or SD.

Naturally, the invention is not limited to the particular form of implementation which has just been described. For example, in this embodiment, the threshold voltage U 'is periodically reset to its minimum value U' _so , this on the one hand in order to be able to decrease it in the event that, due to external disturbances, the rotor has failed more than the N not provided and where, consequently, this tension would have been brought to take too high a value and, on the other hand, to allow the control device to adapt automatically to the possible variations of the characteristics and the conditions of engine operation over time.

It is clear that it would not go beyond the scope of the invention if one were to reduce the reference level to its minimum value each time the control circuit is energized. At the limit, it could even be provided to set the threshold voltage at the value U ' _so only when the motor is started for the first time. Such solutions would of course be less advantageous but they would still represent an improvement compared to known systems where the reference is fixed.

Rather than periodically returning the threshold voltage to its minimum value, it is possible to decrement it gradually, step by step, until engine stops appear and, if the stops are too frequent, to increase it to new.

Furthermore, the missed step counting circuit 201 is provided to prevent the threshold level from being precipitously increased, as soon as a step is not crossed by the rotor, whereas this may be due for example to a shock or to an external magnetic field and not the fact that this level is too low. It is therefore especially useful in the two cases which have just been envisaged, that is to say when the reference voltage is set to its minimum value only when the device is turned on for the first time or when 'it is only reset to this value each time the battery is changed. Indeed, without this counter, by attacking the circuit 202 directly by the signal Q211, the threshold voltage could then be brought very quickly to take its maximum value and the energy consumption of the motor would be unnecessarily high throughout the lifetime of the watch or at least of a battery. On the other hand, if the control device is designed so that the reference level is frequently readjusted, the counting circuit 201 can be eliminated without great inconvenience, by connecting the output of circuit 200 to the first input of circuit 202, because the energy consumption can then be excessive only for a limited period. In addition, it is always possible to reduce energy losses by increasing the frequency of readjustment of the reference level.

On the other hand it is obvious that the invention remains valid for any parameter representative of the operation of the motor other than the voltage induced by the movement of the rotor. It could also be the global induced voltage which includes the effects due to the self of the coil, the current flowing through the motor, the variation of magnetic flux in the stator or any variable resulting from operations mathematics on these quantities.

The block diagram in fig. 1 would remain valid for these different variants except as regards the missed step counting circuit which, as has just been indicated, can in certain cases be omitted and the circuit for calculating the duration of the driving pulses which is not not always necessary, the interruption of these pulses can sometimes be directly controlled by the output of the comparator. Of course the other circuits, at least the measurement circuit 11 and the missed step detector circuit 200 should be adapted to the physical quantity chosen as a representative parameter. For example, in the case where it is the variation in magnetic flux through the coil which is retained as a parameter, circuit 11 can be one of those described in German patent application No. 3132304.

Finally, in the embodiment of the control device according to the invention which has been described, the physical quantity chosen to regulate the duration of the driving pulses was also used for the detection of missed steps. It is clear that this is not mandatory and that different parameters can be used for the two things. If this is the case, the input of the missed step detection circuit 200 must no longer be connected to the output of the measurement circuit 11 but directly to the motor coil or possibly to the motor control circuit.

Claims (17)

1. Method for controlling a stepping motor comprising a rotor and a winding which receives normal driving pulses from a control arrangement associated with the motor so as to cause said rotor to turn when said control arrangement is placed under tension, said method consisting in measuring at the time of each normal driving pulse a physical magnitude representative of the rotor movement and to interrupt said driving pulse at an instant determined as a function of the time required by the measured physical magnitude to attain a reference level, characterized in that it likewise consists in detecting the condition of rotation or non rotation of the rotor in response to said normal driving pulses and to modify said reference level as a function of the information provided by said detection.

2. Method according to claim 1, characterized in that said reference level is adjustable by steps between a minimum and a maximum value and is increased by one step when N steps not effected by the rotor in response to said normal driving pulses have been detected within a predetermined time interval, N being a number equal to or greater than 1.

3. Method according to claim 2, characterized in that said reference level is adjusted to said minimum value when the control arrangement is initially placed under tension.

4. Method according to claim 2, characterized in that said reference level is returned to said minimum value each time said control arrangement is placed under tension.

5. Method according to claim 3 or 4, characterized in that said reference level is likewise periodically returned to said minimum value following each placing under tension of the control arrangement.

6. Method according to any of claims 2 to 5, characterized in that it likewise consists in applying correcting driving pulses to the motor winding of sufficient duration to enable the rotor to recover each step non effected in response to a normal driving pulse.

7. Method according to any of the preceding claims, characterized in that the measured physical magnitude is the tension induced in the winding by the rotor movement.

8. Method according to any of claims 1 to 6, characterized in that the measured physical magnitude is the magnetic flux variation across said winding.

9. Control arrangement for a stepping motor for putting into practice the method according to claim 1 comprising signal generating means producing an output signal each time that the rotor is to make a step, control means for applying normal driving pulses to the motor winding in response to the output signals provided by the signal generating means, means coupled to the motor for measuring during each normal driving pulse the physical magnitude characteristic of the rotor movement and furnishing a measurement signal representative of such magnitude, means for producing a reference sighal corresponding to said reference level, means for furnishing a comparison signal between said measurement signal and said reference signal and means receiving said comparison signal and acting on said control means to interrupt said driving pulse at an instant determined as a function of the time required for said physical magnitude to attain said reference level, characterized in that it further includes detection means (200, 201) for detecting the condition of rotation or non rotation of the rotor in response to the normal driving pulses and in that the means (202) producing said reference signal (U'_s) are conceived so as to be capable of modifying the value of this signal as a function of the information furnished by said detection means.

10. Arrangement according to claim 9, characterized in that said detection means (200, 201) detect the steps not effected by the rotor in response to normal driving pulses, in that the means producing said reference signal (U'_s) are conceived so as to be capable of modifying the value of this signal by steps between a minimum value (U'so) and a maximum value (U'_sp) and in that the value of said reference signal is increased by a step when N steps not effected by the rotor have been detected in a predetermined time interval, N being a number greater than or equal to 1.

11. Arrangement according to claim 10, characterized in that it comprises means (226) for regulating the value of the reference signal (U'_s) to said minimum value (U'so) when it is initially placed under tension.

12. Arrangement according to claim 10, characterized in that it comprises means (226) for restoring the value of the reference signal (U'_s) to said minimum value each time it is placed under tension.

13. Arrangement according to claims 11 or 12, characterized in that it further includes means (203) for periodically restoring the value of the reference signal (U'_s) to said minimum value after said arrangement has been placed under tension.

14. Arrangement according to any of claims 10 to 13, characterized in that it further includes means (215,218) coupled to said detection means for applying correcting driving pulses to the motor winding (10) of sufficient duration to enable the rotor to recover each step not effected in response to a normal driving pulse.

15. Arrangement according to any of claims 10 to 14, characterized in that said detection means (200, 201) receive said measurement signal (U_m) in order to detect the steps not effected by the rotor.

16. Arrangement according to any of claims 9 to 15, characterized in that the measured physical magnitude is the tension induced in the winding by the rotor movement.

17. Arrangement according to any of claims 9 to 15, characterized in that the measured physical magnitude is the magnetic flux variation across said winding.

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