EP0077293B1 - Process and device for controlling a stepping motor in a clock mechanism - Google Patents

Abstract

The present invention concerns a method and a device for controlling a stepping motor of a timepiece, which permit the power of each drive pulse to be adapted to the value of the electromotive force (V) and/or the internal resistance (R*) of the power supply source (10). In accordance with the invention, at a given moment, a value of a chopping rate (Ha) is determined in dependence on the value of the electromotive force V and/or the internal resistance R* of the power supply source (10), said value being stored, and the chopping rate of each control pulse being adjusted to the stored value. The control device comprises means (13) for supplying a chopping signal (M) to a drive circuit (12) of the motor (11). The chopping rate is determined by information contained in a memory (14). The stored information is periodically corrected in dependence on the value of the electromotive force (V) and/or the internal resistance (R*) of the power supply source (10).

Description

The present invention relates to timepieces having a stepping motor, and more particularly a method and a control device for applying to the terminals of the winding of the stepping motor a control signal comprising a sequence of pulses. motor, each of these pulses itself being formed from a series of elementary pulses during which these terminals of the winding are connected to a voltage source, these elementary pulses being separated from each other by periods of interruption during which these terminals are separated from the voltage source.

The book "Theory and Applications of Step Motors", by Benjamin C. Kuo, West Publishing Co., pages 173 to 180 proposes to feed the winding of a stepper motor using a signal command of this type. According to this prior art, the voltage source used for supplying the motor is connected to the terminals of the winding of this motor at the start of each driving pulse. The current in the winding begins to increase, and the power source is disconnected from said winding and the latter is short-circuited as soon as this current reaches a first predetermined value. The current in the winding then begins to decrease, and when it reaches a second predetermined value, the power source is again connected to the terminals of the motor winding whose short circuit is eliminated. The current increases again, and the process described above begins again and continues until the end of the driving pulse. The durations of the elementary pulses and of the interruption periods depend, among other things, on the speed of rotation of the rotor, they are therefore not constant during the duration of a driving pulse. Such a method keeps the current flowing in the motor winding at a substantially constant value.

However, if the voltage of the power source varies, the power supplied to the motor, which is proportional to the product of this voltage and this current, varies in the same way, so that this known method does not make it possible to maintain constant the power supplied to the motor at each driving pulse when using a power source whose electromotive force and internal resistance vary over time.

Patent application GB-A-2 006 995 recommends chopping each drive pulse applied to the motor winding, using two distinct and predetermined values of the chopping rate, the highest value being used only when the motor must provide an abnormally high effort. To this end, this patent recommends using a device detecting the engine load.

This known control device also has the disadvantage of not taking into account fluctuations in the voltage supplied by the power source, fluctuations due to variations in the electromotive force and / or the internal resistance of this source.

However, in electronic timepieces, there is currently a tendency to use a lithium battery as the power source. It is known that the electromotive force supplied by such batteries decreases relatively significantly during the service life of this battery, and that the internal resistance of this battery is subject to significant variations during this service life as well only under the effect of temperature variations. This reduction in electromotive force and / or these variations in internal resistance may cause the engine to stop, and therefore the operation of the timepiece to stop, well before the end of the battery life. To avoid this drawback, the motor must be dimensioned so that it can continue to operate even when the battery provides its lowest electromotive force and has its highest internal resistance. This results in overconsumption of the engine for most of the life of the battery.

The patent application GB-A-2,054,916 recommends supplying the winding of a stepping motor with driving pulses each formed from a series of elementary pulses whose width is determined in dependence on the value of the voltage which is supplied by the power source when the latter is connected to the terminals of resistors of known values. According to this prior art, it is determined, substantially every milliseconds, in which range of values this voltage is found and a motor signal form is chosen from among five predetermined signal forms.

This is therefore a discontinuous adjustment of the power of the driving pulses as a function of the voltage of the power source, and this results in significant variations in the motor torque which can cause lost steps. In addition, this adjustment being discontinuous, it does not allow effective control of the energy of the driving pulses to the load which the motor must drive.

The object of the present invention is to propose a method and a device for controlling a stepping motor of a timepiece making it possible to simply and substantially continuously adapt the power of each driving pulse to the value d 'at least one of the two characteristic quantities of the power source, that is to say the value of the electromotive force and / or that of the internal resistance of this source.

This object is achieved by the method as claimed in claim 1 and the device as claimed in claim 4.

• la figure 1 est un schéma électrique équivalent d'un moteur pas à pas ;
• la figure 2 est un diagramme permettant d'expliquer le procédé selon l'invention ;
• la figure 3 est un schéma synoptique d'un dispositif de commande selon un mode de réalisation de l'invention ;
• la figure 3a est un diagramme qui représente des signaux mesurés en quelques points du schéma da la figure 3 ;
• la figure 4 est un schéma détaillé d'un exemple d'une partie du dispositif de la figure 3, selon un mode de réalisation de l'invention ;
• la figure 5 est un schéma détaillé d'une autre partie du dispositif de la figure 3, selon un mode de réalisation de l'invention ; et
• les figures 5a et 5b sont des diagrammes qui représentent des signaux mesurés en quelques points du circuit de la figure 5 dans deux modes de fonctionnement de ce circuit.
• La figure 1 représente le schéma équivalent d'un moteur pas à pas. L'enroulement du moteur est symbolisé par un enroulement 1 ayant une inductivité de valeur L et une résistance nulle, et par une résistance 2 de valeur R égale à la résistance de l'enroulement du moteur. Un rotor 1a, comprenant généralement un aimant permanent bipolaire cylindrique, est couplé magnétiquement à l'enroulement 1, 2 par un stator non représenté. La tension induite de mouvement, c'est-à-dire la tension qui est induite dans l'enroulement du moteur par la rotation du rotor, est symbolisée sur la figure 1 par une source de tension 3. La valeur de cette tension induite est désignée par U_;. La figure 1 représente également la source d'alimentation du moteur qui est schématisée par une source de tension 4 de résistance interne nulle et de force électromotrice V et par une résistance 5 de valeur R^* égale à la résistance interne de la source réelle servant à alimenter le moteur.

Advantageous embodiments of the invention are contained in claims 2, 3 and 5. The invention will now be described using the attached drawing in which:

• Figure 1 is an equivalent electrical diagram of a stepper motor;
• Figure 2 is a diagram for explaining the method according to the invention;
• Figure 3 is a block diagram of a control device according to one embodiment of the invention;
• FIG. 3a is a diagram which represents signals measured at a few points of the diagram of FIG. 3;
• Figure 4 is a detailed diagram of an example of part of the device of Figure 3, according to an embodiment of the invention;
• Figure 5 is a detailed diagram of another part of the device of Figure 3, according to an embodiment of the invention; and
• FIGS. 5a and 5b are diagrams which represent signals measured at a few points of the circuit of FIG. 5 in two modes of operation of this circuit.
• Figure 1 shows the equivalent diagram of a stepper motor. The motor winding is symbolized by a winding 1 having an inductivity of value L and a zero resistance, and by a resistance 2 of value R equal to the resistance of the winding of the motor. A rotor 1a, generally comprising a cylindrical bipolar permanent magnet, is magnetically coupled to the winding 1, 2 by a stator not shown. The induced movement voltage, that is to say the voltage which is induced in the motor winding by the rotation of the rotor, is symbolized in FIG. 1 by a voltage source 3. The value of this induced voltage is designated by U _; . FIG. 1 also represents the power source of the motor which is shown diagrammatically by a voltage source 4 of zero internal resistance and of electromotive force V and by a resistance 5 of value R ^* equal to the internal resistance of the real source used for power the motor.

In FIG. 1, the motor control circuit is shown diagrammatically by a first switch 6 used to connect and disconnect the source 4, 5 and the motor winding, and by a second switch 7 used to switch this winding on. circuit or to remove this short circuit.

Figure 2 illustrates the manner in which the chopping rate of the driving pulses is determined.

At an instant t0 coinciding with the start of a driving pulse, the switch 6 is closed and the switch 7 is open. The current i in the winding 1 begins to increase. When, at an instant t1, this current reaches a first predetermined value iM, the choice of which will be explained below, the switch 6 is open and the switch 7 is closed. The winding 1, 2 is therefore disconnected from the power source 4, 5 and short-circuited. The current i begins to decrease, and at an instant t2, it reaches a second predetermined value im, the choice of which will also be explained below. The duration Tl m which separates the instants t1 and t2 depends on the electrical and magnetic characteristics of the motor.

At time t2, the switch 6 is again closed and the switch 7 is again open. The short circuit is therefore eliminated, and the source 4, 5 is again connected to the winding 1, 2. The current i begins to increase again. At an instant t3, it reaches the value iM for the second time. The duration T2m which separates the instants t2 and t3 depends on the electrical and magnetic characteristics of the motor as well as on the electromotive force V of the power source 4 and / or on the value R ^* of its internal resistance 5. If this electromotive force V decreases, and / or if this resistance R ^* increases, the time T2m increases.

The durations T1m and T2m are measured and stored. After the instant t3, and until the end of the driving pulse, the switches 6 and 7 are controlled so that the winding is alternately short-circuited and connected to the source 4, 5 for successive periods of duration T1 and T2 respectively equal to Ti m and T2m. In other words, the driving pulse is chopped with a chopping rate Ha defined by Ha = T2m / (T1 m + T2m), and it is composed of a train of elementary pulses having a duty cycle which is also equal to Ha.

The first predetermined value iM can be chosen fairly freely without this choice appreciably influencing the operation of the engine. However, experience has shown that the value iM should preferably be chosen to be substantially equal to the value of the largest current for which the rotor is not yet rotating. If iM is chosen equal to or less than this value, the chopping rate Ha is independent of the load driven by the motor, which would not be the case if iM was chosen at a higher value.

The second predetermined value im can also be chosen quite freely. It suffices that the difference iM - im is small compared to iM, so that the durations T1 m and T2m are also small compared to the time constant r = UR of the motor winding. It will be shown later that this condition is necessary so that the chopping rate determined in the manner described above depends practically only on the characteristics of the power source.

The difference iM - im should not however be chosen too small, so that the durations T1 m and T2m can be measured with sufficient accuracy. In practice, the value of im can be chosen from a range from around 80 to 90% of the value of iM.

dans laquelle U_m est la tension aux bornes du moteur et i est le courant circulant dans son enroulement.In general, the currents and voltages involved in the operation of the motor are linked by the relationship:

in which U _m is the voltage across the motor and i is the current flowing in its winding.

If the value of the current iM is chosen so that the rotor does not yet rotate at time t1, the induced voltage U _i is still zero at this time t1, and equation (1) above can be written :

Between instants t1 and t2, the rotor still does not rotate. The switch 7 is closed and the voltage U _m at the terminals of the motor is therefore zero, provided that the internal resistance of this switch 7 is negligible, which is the case in practice. Equation (2) above can therefore be written:

Between times t2 and t3, the switch 6 is closed, but the rotor still does not rotate. The voltage U _m is equal to (V - R * · i). Equation (2) above therefore becomes:

If the value of the current im is chosen sufficiently close to that of the current iM, the times Ti m and T2m are short compared to the time constant _T = L / R of the motor winding, and it is admissible to replace the term di / dt by a term (―Δi / T1 m) in equation (3) and by a term Δi / T2m in equation (4) with, in both cases, Δi = iM - im. It is likewise possible to replace the term i by its mean value 10 in the intervals t1-t2 and t2-t3, mean value which is equal to (iM + im) / 2.

et

Equations (3) and (4) above then become respectively:

and

et

These equations (5) and (6) give respectively:

and

After time t3, the driving pulse is formed of elementary pulses of duration T2 equal to the measured duration T2m, separated by periods of interruption of duration T1 equal to the measured duration T1 m. The chopping rate Ha of this driving pulse, or the duty cycle of the elementary pulses which compose it, is therefore given by:

By replacing in this equation T1 m and T2m by their values given by equations (7) and (8), and after simplification, we find:

This equation (9) shows that the chopping rate increases when the electromotive force V of the power source decreases and / or that its internal resistance R ^* increases, which is the aim sought.

This hash rate Ha can be determined as described above at the start of each driving pulse. The variations in the electromotive force of the power source and / or its internal resistance are however generally quite slow. This determination can therefore be made at longer intervals. In this case, several successive driving pulses are chopped with the same hash rate.

FIG. 3 shows, by way of example of a device for implementing the method described above, the block diagram of an electronic timepiece comprising a stepping motor 11, and FIG. 3a is a diagram showing signals measured at a few points in the diagram in FIG. 3. This timepiece includes an oscillator circuit 8 generating a time standard signal H having a frequency equal, for example, to 32,768 Hz. The output of the oscillator 8 is connected to the input of a frequency divider circuit 9 developing, from the time standard signal H, various periodic signals. These signals include in particular a control signal J appearing each time the rotor must advance by one step, and a signal I having a period twice that of the signal J. In general, if the timepiece is provided with a second hand, the period of the control signal J is equal to one second.

The timepiece of Figure 3 further includes a pulse forming circuit 15, the output delivers a signal, designated by Z, formed of a series of pulses of the same polarity which pass to the state "1 each time that the signal J itself passes to the state" 1 ", that is to say ie every second.

The length of the pulses of the signal Z is determined by a servo circuit 16 which receives a measurement signal S representative, for example, of the current flowing in the motor. The circuit 16 uses the signal S to deliver a signal N at an instant which depends on the mechanical load driven by the motor. This circuit 16 will not be described in detail since it can be of the type of any one of the many known control circuits. Such a circuit is moreover not essential for the implementation of the method according to the invention, and it could be omitted. In this case, the signal N could be replaced by a signal supplied, for example, by the divider 9. The pulses of the signal Z would then have a constant and predetermined duration.

Each time the signal Z is in the state "1", a drive circuit 12 delivers a driving pulse to the winding 11a of the motor 11. The voltage across this winding is designated by the same reference 11a in the Figure 3a. The energy supplied to the winding 11a during each driving pulse is raised by a power source 10 having, like the source shown in FIG. 1, an electromotive force of value V and an internal resistance of value R ^* .

The polarity of these driving pulses is determined by the logic state of signal I, which alternately takes the state "0 and the state" 1 for 1 second.

The drive circuit 12 is further arranged so that the driving pulses are chopped in response to a chopping signal M formed of pulses having a high frequency. Each time that the signal M is in the state “1”, for example, the drive circuit 12 interrupts the connection between the power source 10 and the winding 11a, and short-circuits the latter. When the signal M is in the state "0", the drive circuit 12 eliminates the short-circuit of the winding 11a and connects the latter to the power source 10.

The signal M is supplied by a circuit 13, an example of which will be described later. The durations of each pulse of this signal M and of the time which separates them, and therefore the hash rate Ha, are determined by the circuit 13 from information which is contained in a memory 14. The circuit 13 comprises in in addition to means for periodically correcting this information as a function of the measurement signal S supplied by the drive circuit 12.

The periodicity of this correction can be equal to or greater than the period of the motor impulses.

FIG. 4 represents an example of a diagram of the circuits 12 and 15 of FIG. 3. The circuit 15 simply comprises, in this example, a flip-flop 39 of type T whose clock input T receives the signal J delivered by the divider of frequency 9 in FIG. 3 at a frequency of 1 Hz. The reset input R of flip-flop 39 receives the signal N of the servo circuit 16 of FIG. 3. The output Q of this flip-flop 39 therefore passes in state "1" when signal J changes to state "1", that is to say each time the rotor must turn one step, and returns to state "0" when the circuit 16 delivers the signal N at a determined time so that the duration of the signal Z, which is delivered by this output Q of the flip-flop 39, is equal to the optimum duration of the driving pulse. As already mentioned, circuit 16 could be omitted. The input R of the flip-flop 39 would then be connected to an output, not shown, of the divider 9, chosen so that the duration of the signal Z is equal, for example, to 7.8 milliseconds.

The circuit 12 of FIG. 3 comprises, in this example, a combinatorial circuit 43 formed by four AND gates 431 to 434, two OR gates 435 and 436 and two reversers 437 and 438. The winding 11 a of the motor is connected , conventionally, in a circuit formed by four transmission doors 44 to 47 connected between the + V terminal of the power source 10 and the ground.

Two other transmission doors 48 and 49 each connect one of the terminals of the winding 11a to a first terminal of a measurement resistor 17, the second terminal of which is connected to ground. The voltage present on the first terminal of this resistor 17 constitutes the signal S mentioned above.

A transmission door 50 is connected in parallel with the resistor 17. It is controlled by a signal X supplied as the case may be by the circuit 15 or by the circuit 13. When the circuit of FIG. 2 includes the servo circuit 16, the signal X can be supplied by the forming circuit 15 so that the gate 50 is blocked during the driving and conducting pulses between them. The servo circuit 16 then uses this signal S to adjust the length of the pulses Z, and therefore the length of the driving pulses, to the mechanical load driven by the rotor.

When the circuit of FIG. 2 does not include a servo circuit 16, the signal X can be supplied by the circuit 13, so that the gate 50 is only blocked when this circuit 13 uses the signal S to modify the information contained in memory 14 and that this door 50 is conductive the rest of the time. This case will be described in more detail later.

• - lorsque le signal Z est à l'état « 0 », c'est-à-dire entre les impulsions motrices, les électrodes de commande des portes 44 à 49 sont toutes à l'état « 0 », quel que soit l'état des signaux I et M. Toutes ces portes sont donc bloquées et l'enroulement 11a est séparé de la source d'alimentation ;
• - lorsque le signal Z est à l'état « 1 », c'est-à-dire pendant les impulsions motrices, et que le signal M est à l'état « 0 », les portes 44 et 48 ou 45 et 49 sont conductrices, selon l'état « 0 ou « 1 » du signal 1. Toutes les autres portes sont bloquées. La source d'alimentation 10 est donc reliée à l'enroulement 11a a par l'intermédiaire des portes 44 et 48 ou 45 et 49, et un courant circule dans l'enroulement 11a dans le sens de la flèche 11 b ou dans le sens inverse. Cette situation est celle qui se présente entre les périodes d'interruption, pendant les impulsions élémentaires ; et
• - lorsque le signal Z est à l'état « 1 et que le signal M est également à l'état « 1 », les portes 47 et 48 ou 46 et 49 sont conductrices, selon l'état « 0 » ou « 1 » du signal I. Toutes les autres portes sont bloquées. La source d'alimentation est donc déconnectée de l'enroulement 11a qui est mis en court-circuit. Cette situation est celle qui se présente pendant les périodes d'interruption de l'impulsion motrice.

The control electrodes of the doors 44 to 49 are connected to the outputs of the combinational circuit 43 whose inputs receive the signals I, Z and M respectively. This combinative circuit will not be described in more detail, because it is easy to see, at the using Figure 4, that:

• when the signal Z is in the state "0", that is to say between the driving pulses, the control electrodes of the doors 44 to 49 are all in the state "0", whatever the state of signals I and M. All these doors are therefore blocked and the winding 11a is separated from the power source;
• - when signal Z is in state "1", that is to say during the driving pulses, and signal M is in state "0", gates 44 and 48 or 45 and 49 are conductive, depending on the state "0 or" 1 "of signal 1. All other doors are blocked. The power source 10 is therefore connected to the winding 11a a via the doors 44 and 48 or 45 and 49, and a current flows in the winding 11a in the direction of the arrow 11 b or in the direction reverse. This situation is that which occurs between periods of interruption, during elementary impulses; and
• - when signal Z is in state "1 and signal M is also in state" 1, gates 47 and 48 or 46 and 49 are conductive, depending on state "0" or "1" signal I. All other doors are blocked. The power source is therefore disconnected from the winding 11a which is short-circuited. This situation is that which occurs during periods of interruption of the motor impulse.

If, in addition, the door 50 is blocked by a state “0” of the signal X, during a driving pulse, the current which passes through the winding 11a also passes through the resistor 17. The voltage produced by this current at this resistor 17 constitutes the signal S.

It is obvious that this combinatorial circuit 43 could be easily modified so that the doors 44 and 45, for example, are both conductive and that the winding is therefore short-circuited between the driving pulses. Such an arrangement is often used to quickly brake the oscillations of the rotor around its equilibrium position, at the end of a driving pulse.

FIG. 5 shows by way of example the diagram of an embodiment of the circuit 13 of FIG. 3.

This circuit comprises two counters 54 and 55, which together form the memory 14 of the circuit of FIG. 3. The clock inputs CL of these counters 54 and 55 are connected respectively to the outputs of two AND gates 56 and 57. These gates 56 and 57 each have a first input which receives the signal H from the output of the oscillator 8, not shown in this figure, a second input connected to the output Q of a flip-flop 59 of type T, and a third input connected to the exit Q of another rocker, 60, also of type T.

The doors 56 and 57 have a fourth input connected directly, respectively via an inverter 65, to the output 52f of a hysteresis circuit which will be described later. This output 52f is also connected to the clock input T of the flip-flop 59 and to a first input of a NAND gate 71, a second input of which is connected to the output Q of the flip-flop 60.

The output Q of the flip-flop 59 is connected to the clock input T of the flip-flop 60. The output Q of this flip-flop 60 is connected to the first inputs of a NAND gate 70 and an AND gate 522, as well as at the control input of the transmission door 50 (FIG. 4). This output Q of the flip-flop 60 delivers the signal X mentioned above.

The reset inputs R for flip-flops 59 and 60 as well as counters 54 and 55 are connected to the output Q of a flip-flop 371, of type T, which forms a timer circuit 37 with a counter 372 whose input d the clock CL receives the signal J from the frequency divider 9 (FIG. 3). The reset input R of flip-flop 371 as well as a second input of gate 522 also receive the signal H.

The outputs of the counters 54 and 55, which are designated together, for each counter, by the reference Si, are connected to the preselection inputs of two reversible counters 66 and 67, designated together, for each counter also, by the reference Pi. U / D inputs for controlling the counting direction of these counters 66 and 67 permanently receive a logic signal “1 •, so that these counters operate continuously as down counters. The clock inputs CL of these counters 66 and 67 are connected to the output of gate 522.

The PE preselection control input of the counter 67 is connected to the output of a NAND gate 69 whose inputs are connected respectively to the outputs of doors 70 and 71. The PE preselection control input of the counter 66 is also connected to the output of door 69, but via an inverter 68.

The counters 66 and 67 each have an output C which delivers a short pulse when their content reaches the value zero. These outputs C are respectively connected to two inputs of an OR gate 73, a third input of which is connected to the output Q of the flip-flop 371. The output of this gate 73 is connected to the clock input T of a flip-flop 710 of type T. The output Q of this flip-flop 710 is connected to a second input of the gate 70, and its input R for resetting to zero is connected, via an inverter 711, to the output Q of flip-flop 39 (FIG. 4) which delivers the signal Z. This signal Z is also applied to a third input of gate 522.

The output of door 69 delivers the interrupt control signal M to the drive circuit 12 (Figures 3 and 4).

The hysteresis circuit 52 comprises, in a conventional manner, a differential amplifier 52b, a reference voltage source 52c and a voltage divider formed by two resistors 52d and 52e. This voltage divider is connected between the input 52a of the circuit 52, which receives the signal S from the measurement resistor 17 (FIG. 4), and the output of the amplifier 52b which constitutes the output 52f of the circuit 52. The non-inverting input of this amplifier 52b is connected to the connection point of resistors 52d and 52e, and its inverting input is connected to the output of reference source 52c.

The gain of the amplifier 52b, the values of the resistors 52d and 52e as well as of the resistor 17, and the value of the reference voltage supplied by the source 52c are chosen so that when the transmission gate 50 (FIG. 4) is blocked and the current in the winding 11a increases, starting from its zero value for example, the output 52f of the circuit 52 goes to the state "1 at the moment when this current reaches the value iM defined above and that, when this current decreases from a value greater than or equal to this value iM, this output 52f of circuit 52 does not return to the state "0" only when this current reaches the value im also defined above.

The operation of the circuit of FIG. 5 will now be described in detail with the aid of FIG. 5a in the case of a normal driving pulse and with the aid of FIG. 5b in the case of a driving pulse during which new values of T1m and T2m are measured and stored.

It will be shown below that, in normal operation, the Q output of the flip-flop 59 is in the "0" state and the Q output of the flip-flop 60 is in the "1" state. The signal X is therefore in state "1", the gate 50 (FIG. 4) is conductive, and the signal S remains permanently at zero voltage. On the other hand, the doors 56 and 57 are blocked and the inputs CL of the counters 54 and 55 are maintained in the "0" state. In addition, the output of gate 71 is in state "1", and the output of gate 69, which delivers the signal M, takes the same state as the output Q of flip-flop 710.

It will also be shown below that the state of the outputs of the counter 54 corresponds to a number expressed in binary code, designated by N1 in FIG. 5a, which is equal to the quotient of the duration T1 m defined above (FIG. 2 ) divided by the frequency of the signal H. Similarly, the state of the outputs of the counter 55 corresponds to a number, also expressed in binary code, which is designated by N2 in FIG. 5a and which is equal to the quotient of the duration T2m defined above (figure 2) divided by the frequency of the signal H.

Between the driving pulses, signal Z is in the state "0". The gate 522 is therefore blocked, and the clock inputs CL of the counters 66 and 67 are in the "0" state. The reset input R of flip-flop 710 is in state "1", and the output Q of this flip-flop 710 is therefore in state "0".

During the driving pulses, signal Z is in the state "1". The input R of the flip-flop 710 is therefore in the "0" state, and the pulses of the signal H, having a frequency of 32,768 Hz, are transmitted to the clock inputs CL of the counters 66 and 67.

When the output Q of the flip-flop 710, and therefore the signal M, are in the state "0", that is to say during each of the elementary pulses which form the driving pulses, the preselection command input PE of counter 66 is in state "1". The content N1 of the counter 54 is therefore imposed on the counter 66, which remains blocked in this state.

The counter preselection command input PE of the counter 67 is on the other hand in the state “0”, and this counter counts the pulses of the signal H from a corresponding state, as will be shown below, with the content N2 counter 55.

When the content of this counter 67 reaches the value zero, the output C of this counter 67 delivers a short pulse, which is applied to the input T of the flip-flop 710 via the gate 73. The output Q of this flip-flop 710 goes to state "1", and signal M therefore also goes to state "1".

The circuit 12 (FIG. 4) interrupts the current driving pulse in response to this state "1 of the signal M. In addition, the preselection command input PE of the counter 67 changes to the state" 1 ", and the N2 content of counter 55 is transferred to counter 67, which remains blocked in this state. Finally, the preselection command input PE of the counter 66 passes to the state “0”, and this counter begins to count the pulses of the signal H from the state which it has at this instant, it is ie the state corresponding to the content N1 of the counter 54.

When the content of counter 66 reaches the value zero, the output C of this counter 66 delivers a short pulse which is applied to the input T of flip-flop 710. The output Q of this flip-flop 710 and the signal M revert to state "0", and the process described above begins again, as long as the output of timer 37 remains in state "0".

The duration during which the signal M remains in the state "0", that is to say the duration T2 of each elementary pulse, is equal to the product of the period of the signal H by the number corresponding to the content of the counter 67 at the moment when the signal M goes to the state "0". As this number is equal to the number N2 corresponding to the content of the counter 55, this duration T2 is equal to the duration T2m defined above. Similar reasoning shows that the duration during which the signal M remains in the state "1", that is to say the duration T1 of each period of interruption of the driving pulse, is equal to the duration T1m defined above.

When the output of counter 372 goes to state "1", the Q output of flip-flop 371 goes to state "1". This output Q returns to state “0” about 15 microseconds later, in response to the passage to state “1” of signal H. This pulse, which constitutes a periodic recalibration signal designated by RZ, puts the counters 54 and 55 to zero, and puts the flip-flops 59 and 60 in the state where their outputs Q are both in the state "0". The doors 56, 57 and 522 are therefore blocked, and the clock inputs CL of the counters 54, 55, 66 and 67 are maintained in the state "0". On the other hand, the output Q of flip-flop 710 is set to the state "1". The outputs of gates 70 and 71 are both in state "1", and the signal M, present at the output of gate 69, is therefore in state "0".

The signal Z also goes to state "1 at the instant when the output of counter 372 goes to state" 1 ". As the signal M is in the state “0”, the drive circuit 12 connects the power source to the winding 11a (FIG. 4). The transmission door 50 (FIG. 4) being blocked by the signal X which is in the state “0”, the current which begins to circulate in the winding 11a also passes through the resistor 17. When this current reaches for the first times the value iM, the output 52f of the hysteresis circuit 52 and the output Q of the flip-flop 59 pass to the state "1". Simultaneously the output of gate 71 goes to state "0", and signal M goes to state "1". The drive circuit 12 therefore interrupts the connection between the power source 10 and the winding 11a, and short-circuits the latter. The current flowing in this winding 11a and in the resistor 17 begins to decrease.

At the same time, the gate 56 begins to let pass the pulses of the signal H, which are counted by the counter 54. After a time T1m which depends only on the electrical and magnetic characteristics of the motor, the current in the winding 11a reaches the im value. At this instant, the output 52f of the hysteresis circuit 52 goes to the state "0". The door 56 is therefore blocked. The content of the counter 54 at this instant is equal to the product of the time T1 m and the frequency of the signal H.

Simultaneously, the output of gate 71 returns to state "1", and signal M returns to state "0". The drive circuit 12 therefore re-establishes the connection of the winding 11a with the power source 10, and the current in this winding 11a begins to increase again. In addition, the gate 57 begins to allow the pulses of the signal H to pass, which are counted by the counter 55. At the same time, the preselection command input PE of the counter 66 changes to state “1”, and the content of counter 54 is transferred to this counter 66 which remains blocked in this state.

After a time T2m which depends both on the electrical and magnetic characteristics of the winding 11a and on the electromotive force. V of the power source 10 and its internal resistance R ^* , the current in the winding 11a reaches the value iM for the second time. At this instant, the output 52f of the hysteresis circuit 52 returns to the state "1". The Q output of flip-flop 59 therefore returns to state "0", and the Q output of flip-flop 60 changes to state "1". Gate 57 is blocked by the state “0” of output Q of flip-flop 59. At this instant, the content of counter 55 is equal to the product of time T2m and the frequency of signal H.

The output of gate 71 is set to state "1" by the state "0" of output Q of the flip-flop 60. From this instant, the signal M again becomes dependent on the state of output Q of the flip-flop 710, which is state "1" at this time. The drive circuit 12 therefore interrupts the driving pulse.

The doors 56 and 57 are blocked by the state “0 of the output a of the flip-flop 60. The transmission door 50 (FIG. 4) is however made conductive by the state“ 1 ”of the output Q of this flip-flop 60, and short-circuits the resistor 17. The signal S therefore becomes zero again.

The output Q of the flip-flop 60 being in state "1", the gate 522 allows the pulses of signal H to pass. These pulses are counted down by the counter 66 whose preselection command input PE is in the state " 0 ".

From this moment, the circuit of Figure 5 operates as described above. The signal M alternately takes the state "1 and the state" 0 during times T1 and T2 which are equal, respectively, to the times T1 m and T2m measured in the manner described above. As the time T2m depends directly on the voltage V of the power source 10 and / or its internal resistance R ^* , the chopping rate of the driving pulses also depends on these quantities.

The circuit of FIG. 5 therefore makes it possible to implement the method described above.

It is obvious that many modifications could be made to this circuit of FIG. 5 without departing from the scope of the invention. For example, the frequency of the signal H, which determines the precision with which the times T1 m and T2m are measured, could be chosen at a different value. On the other hand, still for example, the counter 372 could be deleted. The signal J would then be directly applied to the input T of the flip-flop 371. The determination of the hash rate Ha would therefore be made in this case at the start of each driving pulse.

Claims (5)

1. A method of controlling a stepping motor having a winding (11a) and a rotor (1a) magnetically coupled with said winding (11a), which comprises applying to said winding (11a) a drive pulse consisting of a succession of elementary pulses during which said winding (11a) is connected to a supply source (10) having first and second characteristic magnitudes respectively consisting of its electromotive force (V) and of its internal resistance (R^*), said elementary pulses being separated from one another by periods of interruption during which said winding (11a) is separated from said supply source (10), characterised in that the periods of interruption that follow the first of said periods of interruption all have a first duration (T1) proportional to a first memorised number (N1) and the elementary pulses that follow the second of said elementary pulses all have a second duration (T2) proportional to a second memorised number (N2), and in that it further comprises determining said first memorised number (N1) during said first period of interruption and said second memorised number (N2) during said second elementary pulse in dependence on the value of at least one of said characteristic magnitudes (V, R^*).

2. A method as in claim 1, characterised in that it comprises determining said first and second memorised numbers (N1, N2) by connecting said source (10) and said winding (11a) at the start of said drive pulse, by detecting a first instant (t1) when the current (i) flowing in the winding (11 a) reaches for the first time a first predetermined value (iM), by disconnecting said source (10) from said winding (11a) and substantially short-circuiting the latter as from said first instant (t1), by detecting a second instant (t2) when said current (i) reaches a second predetermined value (im) less than said first predetermined value (iM) for the first time after said first instant (t1), by measuring a first time span (T1m) between said first instant (t1) and said second instant (t2), by cutting out said short-circuiting and reconnecting said source (10) and said winding (11a) as from said second instant (t2), by detecting a third instant (t3) when said current (i) reaches for the second time said first predetermined value (iM), by measuring a second time span (T2m) between said second instant (t2) and said third instant (t3), and by giving to said first memorised number (N1) a value proportional to the value of said first time span (Tl m) and to said second memorised number (N2) a value proportional to the value of said second time span (T2m), the factors of proportionality between said memorised numbers (N1, N2) and said first and second durations (T1, T2) on the one hand, and between said memorised numbers (N1, N2) and said first and second time spans (T1 m, T2m) on the other hand being all equal.

3. A method as in claim 1, characterised in that it further comprises applying to said winding a second drive pulse consisting of a plurality of elementary pulses all having said first duration (T1) and separated by periods of interruption all having said second duration (T2).

4. A device for controlling a stepping motor having a winding (11a) and a rotor (1a) magnetically coupled with said winding (11a), which comprises :

a supply source (10) having first and second characteristic magnitudes respectively consisting of its electromotive force (V) and of its internal resistance (R^*) ;

means (8, 9) for producing a control signal (J) whenever the rotor (1a) is required to rotate one step ; and

means (12 to 15 ; 39, 43 to 47, 54, 55, 66, 67, 710) responsive to said control signal (J) for producing and for applying to said winding (11a) a drive pulse consisting of a plurality of elementary pulses during which said winding (11a) is connected to said supply source (10), said elementary pulses being separated from one another by periods of interruption during which said winding (11a) is separated from said supply source (10) ; characterised in that said means (12 to 15 ; 39, 43 to 47, 54, 55, 66, 67, 710) for producing and for applying to said winding (11a) said drive pulse include means (14 ; 54, 55) for memorising first and second numbers (N1, N2), means (12, 13, 15; 39, 43 to 47, 66, 67, 710) for giving to the periods of interruption following the first of said periods of interruption a duration (T1) proportional to said first memorised number (N1) and to the elementary pulses following the second of said elementary pulses a duration (T2) proportional to said second memorised number (N2), and in that the device further comprises means (37, 52, 56, 57, 59, 60) responsive to said control signal (J) for determining said first memorised number (N1) during said first period of interruption and said second memorised number (N2) during said second elementary pulse in dependence of the value of at least one of said characteristic magnitudes (V, R^*).

5. A device as in claim 4, characterised in that said means (15 ; 54, 55) for memorising first and second numbers (N1, N2) include a first counter (54) having a state representative of said first number (N1) and a second counter (55) having a state representative of said second number (N2), and in that said means (37, 52, 56, 57, 59, 60) for determining said first and second numbers (N1, N2) include:

means (37) for producing a recalibration signal (RZ) at the start of each drive pulse ;

means (52) for producing a measurement signal with a first state when the current (i) flowing in said winding (11a) reaches when increasing a first predetermined value (iM) and with a second state when the current (i) reaches when decreasing a second predetermined value (im) less than said first predetermined value (iM) ;

means (59, 60) for successively causing the connection of said winding (11a) and of said supply source (10) in response to said recalibration signal (RZ), the interruption of said connection at a first instant (t1) when said measurement signal assumes its first state for the first time after said recalibration signal (RZ) and again the connection of said winding (11a) and of said supply source (10) at a second instant (t2) when said measurement signal assumes its second state for the first time after said first instant (t1) ;

means (56) for supplying to said first counter (54) a first number of pulses proportional to a first time span (T1 m) between said first and second instants (t1, t2), said first number (N1) being thus proportional to said first time span (T1m) after said second instant (t2) ; and

means (57) for supplying to said second counter (55) a second number of pulses proportional to said second time span (T2m) between said second instant (t2) and a third instant (t3) when said measurement signal assumes for the second time its first state, said second number (N2) being thus proportional to said second time span (T2m) after said third instant (t3) ; the factors of proportionality between said memorised numbers (N1, N2) and said first and second durations (T1, T2) on the one hand, and between said memorised numbers (N1, N2) and said first and second time spans (Tl m, T2m) on the other hand being all equal.

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