EP0253153A1 - Method and device for controlling a stepping motor - Google Patents

Abstract

The method comprises measuring the quantity of electrical energy Eme converted into mechanical energy by the motor during a driving pulse, determining the time taken by this quantity of energy Eme to reach a reference value Eref, and the interruption of the driving impulse dependent on this time. The device comprises means (5 to 15) for measuring this quantity of energy Eme, means (19, 20, 22) for determining the time taken by this quantity of energy to reach this reference value Eref, and means (23 to 26) to cause the interruption of the motor impulse depending on this time.

Description

An object of the present invention is a method of controlling a stepping motor comprising a coil and a rotor magnetically coupled to said coil, said method comprising applying to said coil a driving pulse each time said rotor has to turn one step.

Another object of the present invention is a control device implementing this method.

There are many methods for decreasing the consumption of a stepper motor by adjusting the amount of electrical energy supplied to the motor during a drive pulse to the resistive torque that the rotor must overcome. Since this torque cannot be measured directly, these processes actually adjust this quantity of electrical energy as a function of the measurement or calculation of a physical quantity whose value or variation as a function of time depends more or less directly on this couple.

The determination of the resistive torque applied to the rotor during a driving pulse can be made after the end of this pulse as, for example, in patent US-A-4,212,156. In this patent, the variation of the current induced in the coil of the motor by the oscillations of the rotor after the end of a driving pulse is taken as a measurement of this torque, and the duration of the following driving pulses is modified, if necessary, according to the result of this measurement.

The determination of the resistive torque applied to the rotor can also be made during each driving pulse as, for example, in patent application EP-AO 060 806. In this application, it is the speed of variation of the voltage induced in the coil of the motor by the rotation of the rotor which is taken as a measure of this torque.

These methods, as well as the many others which cannot be mentioned here, all have the drawback that the physical quantity which they use as a measure of the resisting torque is not really representative of this torque.

As a result, the control of a stepping motor according to any of the known methods can hardly be optimal. This means that if the device implementing the chosen method is arranged in such a way that the motor works correctly in all possible situations, the consumption of this motor will generally be quite clearly greater than its minimum theoretical consumption. If we try to modify the characteristics of the control circuit so that the consumption of the motor decreases and approaches its theoretical minimum, then the operating safety of this motor decreases, that is to say that its rotor no longer turns correctly in response to each motor impulse.

It is sometimes necessary to send a driving impulse to a stepping motor such that it certainly causes the rotation of the rotor, even if the resistive torque applied to the latter has its maximum value.

This case arises in particular when the engine is controlled according to a method such as that described in patent US-A-4,272,837 for example.

Such a method consists in particular in applying to the motor a long-lasting pulse, called the catch-up pulse, when an adequate circuit has detected that its rotor has not rotated in response to a normal driving pulse, of short duration.

The duration of the catch-up pulse is obviously determined so that it causes the rotation of the rotor even if the resistive torque applied to the latter has its maximum value.

However, it may happen that the cause of a non-rotation of the rotor in response to a normal driving pulse is only momentary, and that the torque applied to the rotor during the next catching pulse is low. In such a case, the amount of electrical energy supplied to the motor during this make-up pulse is much too high, and it is possible that the motor rotor takes several steps, instead of a threshold, in response to this pulse. catching up.

Detection of the rotation or non-rotation of the rotor which is necessary in the control methods which have just been mentioned can be done in various ways.

Thus, for example, in the method described in US Pat. No. 4,272,837 mentioned above, this detection is carried out by applying to the stepper motor a very short detection pulse some time after the end of each pulse. motor. The amplitude of the current flowing in the motor coil at the end of this detection pulse makes it possible to determine whether the rotor has rotated or not in response to the previous driving pulse.

The difference between the currents flowing in the coil in either case, rotation or non-rotation of the rotor, is however small, which makes it difficult to reliably detect this non-rotation. In addition, the measurement of the current may be distorted if the rotor is in motion when the detection pulse is applied to the motor, either because this rotor has not yet finished oscillating around its equilibrium position, or because it has been set back in motion, for example by a shock.

There are other methods for detecting whether or not the rotor of the stepper motor has rotated in response to a driving pulse. These methods will not be described here, except to point out that they generally have the same drawbacks as the method described above.

An object of the present invention is to provide a method of controlling a stepping motor which does not have the drawbacks of the methods mentioned above and which makes it possible, depending on the manner in which it is implemented, to reduce consumption of the stepping motor practically to its absolute minimum, or to rotate the motor rotor one step and only one, with great safety, and whatever the resistive torque applied to this rotor, or allow safe detection of the rotation or non-rotation of this rotor in response to a driving impulse.

Another object of the present invention is to provide a device for implementing this method.

These objects are respectively achieved by the claimed method and device.

• -la figure 1 représente le schéma d'un circuit qui met en oeuvre le procédé selon l'invention pour ajuster la durée des impulsions motrices en fonction du couple résistant appliqué au rotor du moteur;
• -la figure 2 est un diagramme illustrant le fonctionnement d'une partie du circuit de la figure 1;
• -la figure 3 représente la variation de la consommation d'un moteur pas à pas commandé par le circuit de la figure 1 en fonction du courant de référence, pour plusieurs couples résistants appliqués au rotor;
• -la figure 4 représente la variation de la durée optimale de l'impulsion en fonction du courant de référence, pour plusieurs couples résistants appliqués au rotor;
• -la figure 5 représente la relation entre le temps mis par la quantité d'énergie Eme pour atteindre la valeur de référence E_ref et la durée optimale de l'impulsion motrice;
• -la figure 6 est un diagramme illustrant le fonctionnement d'une autre partie du circuit de la figure 1;
• -la figure 7 représente une autre forme d'exécution d'un circuit de mise en oeuvre du procédé selon l'invention;
• -la figure 8 est un diagramme illustrant le fonctionnement du circuit de la figure 7;
• -la figure 9 représente le schéma d'un circuit qui peut être associé au circuit de la figure 1 pour déterminer si le rotor du moteur tourne correctement ou non en réponse à une impulsion motrice; et
• -les figures 10a et 1 Ob sont des diagrammes illustrant le fonctionnement du circuit de la figure 9.

The invention will be described below using the attached drawing in which:

• FIG. 1 represents the diagram of a circuit which implements the method according to the invention for adjusting the duration of the driving pulses as a function of the resistive torque applied to the rotor of the motor;
• FIG. 2 is a diagram illustrating the operation of part of the circuit of FIG. 1;
• FIG. 3 represents the variation of the consumption of a stepping motor controlled by the circuit of FIG. 1 as a function of the reference current, for several resistive torques applied to the rotor;
• FIG. 4 represents the variation of the optimal duration of the pulse as a function of the reference current, for several resistive couples applied to the rotor;
• FIG. 5 represents the relationship between the time taken by the quantity of energy Eme to reach the reference value E _ref and the optimal duration of the driving pulse;
• FIG. 6 is a diagram illustrating the operation of another part of the circuit of FIG. 1;
• FIG. 7 represents another embodiment of a circuit for implementing the method according to the invention;
• FIG. 8 is a diagram illustrating the operation of the circuit of FIG. 7;
• FIG. 9 represents the diagram of a circuit which can be associated with the circuit of FIG. 1 to determine whether the rotor of the motor turns correctly or not in response to a driving pulse; and
• FIGS. 10a and 1 Ob are diagrams illustrating the operation of the circuit of FIG. 9.

Generally, it is known that the rotor of a stepping motor is permanently subjected to a resistive torque Tr which opposes the rotation of this rotor.

This resistant torque Tr is produced by the friction couples of the rotor itself and of the mechanical elements which it drives in their bearings and between them, by the eddy currents and the hysteresis phenomena which are produced in the stator of the motor. by the variations of the magnetic field which crosses this stator, and by the positioning torque of the rotor, as long as this rotor has not exceeded the angular position of unstable equilibrium where this positioning torque becomes a driving torque.

This resisting torque Tr is therefore variable as a function of time in a random manner, and it can take any value between a minimum value Tr _min and a maximum value Tr _max which both depend on the characteristics of the engine and of the mechanical elements. which it entails and which can be determined analytically or by tests.

Each value of this resistive torque Tr corresponds to a quantity of mechanical energy Emm which is that which the motor must supply, at a minimum, so that its rotor turns by one step. In particular, the values Tr _min and Tr _max of this resistive torque correspond respectively to the values Emm _min and Emm _max of this quantity of energy. This resistive couple Tr and this quantity of energy Emm are linked by a mathematical relation which will not be given here because it is well known to specialists and has moreover no direct relation with the invention.

dans laquelle:

On the other hand, we also know that the electrical energy Ep _ox supplied by the motor power source between the start of a driving pulse located at an instant t _o and any instant t _x satisfies the following equation:

in which:

The measurement of time T therefore makes it possible, using this relation, to determine the optimal duration τ of the driving pulse.

The same principle can be used to determine whether the motor rotor has turned correctly or not in response to a driving impulse. Indeed, if the amount of energy Eme converted by the motor reaches a predetermined value before an equally predetermined time has elapsed, this means that the rotor has correctly taken its step. If this quantity of energy Eme does not reach this predetermined value in this time, it means that the rotor has not rotated.

It can be seen that the measurement of the quantity of electrical energy Eme which is converted into mechanical energy by the motor can serve as a basis, in a manner which will be specified below, for effectively controlling this motor in all the cases mentioned above. .

On sait en outre que:

dans lesquelles:

• -U est la tension de la source d'alimentation du moteur;
• -i_s(t) est le courant fourni par cette source;
• -i_m(t) est le courant circulant dans la bobine du moteur; et
• -R et L sont respectivement la résistance et l'inductance de la bobine du moteur.

From equation (1) above, it is easy to draw that:

We also know that:

in which:

• -U is the voltage of the motor power source;
• -i _s (t) is the current supplied by this source;
• -i _m (t) is the current flowing in the motor coil; and
• -R and L are respectively the resistance and the inductance of the motor coil.

Equation (2) above can therefore be written:

It is possible to design an electronic circuit capable of providing a signal representative of the amount of Emeox energy.

This circuit can for example comprise means for producing signals proportional to the currents i _s and i _m , as well as analog or digital circuits making it possible to carry out the various operations of equation (6). This circuit is not shown because its realization follows directly from 'equation (6).

FIG. 1 represents in particular the diagram of an exemplary circuit also making it possible to supply a signal representative of the quantity of energy Eme _0x , in a particular case where the stepping motor is controlled so that the current which flows in its coil is substantially constant and equal to a reference current l _ref (see Figure 2).

In the case illustrated in FIG. 1, the motor, designated by the reference M, is supplied by a driving pulse generator circuit 1 which will not be described in detail here since it may be similar to a circuit having the same function and which is described in patent application EP-AO 057 663.

This forming circuit 1 is arranged so as to trigger a driving pulse IM at each instant, designated by t ₀ as above, where the rotor of the motor M must turn one step, in response to the transition from the logic state " 1 "" in logic state "O" of a control signal which it receives on its input 1a.

In this example, this control signal is formed by periodic pulses having a frequency of 1 Hz, which are supplied by an output 2a of a frequency divider 2 whose input 2b is connected to the output 3a of an oscillator 3 controlled by a quartz 4. It is obvious that, in other applications, the control signal applied to the input 1 a of the formatter 1 may not be periodic.

The output signal from oscillator 3 has a frequency of 32,768 Hz. In addition to its output 2a, the divider 2 has intermediate outputs 2c to 2k delivering signals having frequencies of 16,384 Hz, 8,192 Hz, 4 respectively '096 Hz, 2048 Hz, 1'024 Hz, 512 Hz, 256 Hz, 128 Hz and 64 Hz.

These circuits 2 and 3 will not be described in detail here, because they are conventional and well known to specialists.

The forming circuit 1 is arranged so as to connect, at each instant ta, the coil of the motor M to a source of power supply, not shown. From this instant t ₀ , the voltage U _m across the motor coil M is therefore equal to the voltage U of this power source.

The current im which begins to circulate in the coil at this instant t ₀ (see FIG. 2) is measured by a measurement circuit 5 which produces a voltage proportional to this current i _m . This measurement circuit 5 will also not be described here, because it can be similar to a circuit having the same function and which is described in patent application EP-A-0 057 663 already mentioned.

The circuit of Figure 1 further includes a source 6 which produces a voltage proportional to the reference current l _ref mentioned above.

The proportionality relationships between the current i _m and the voltage produced by the circuit 5 on the one hand, and between the current l _ref and the voltage produced by the source 6 on the other hand are identical.

The voltages produced by the circuit 5 and by the source 6 are applied to an analog comparator 7, of the conventional type. Since the proportionality ratios mentioned above are equal, it can be said that the comparator 7 compares the current i _m with the current l _ref .

The comparator 7 delivers at its output 7a a signal which takes the logic state "1" when the current i _m is less than the current l _ref and the logic state "O" otherwise.

The output 7a of the comparator circuit 7 is connected to the input D of a flip-flop 9 of type D whose clock input CL receives the signal having a frequency of 8'192 Hertz provided by the output 2d of the divider circuit 2 and which, for a reason which will be made evident from the description, will be called the sampling signal. The instants when this sampling signal goes from logic state "1" to logic state "0" will be called sampling instants.

Conventionally, the output Q of the flip-flop 9 takes the same state as its input D each time its input CL goes from logic state "1" to logic state "O". It is also the same for the other D type flip-flops which will be mentioned below.

Just after the instant to, the current i _m is less than the current l _ref . The output 7a of the comparator 7 and the output Q of the flip-flop 9 are therefore in the state "1".

When the current i _m becomes greater than the current 1 _ref , the output 7a of the comparator 7 goes to the logic state "O".

At the first sampling instant following this passage from the output 7a of the comparator 7 to the state "O", which is designated by the reference t ₁ , the output Q of the flip-flop 9 also changes to the state "O".

The circuit 1, an input 1b of which is connected to the output Q of the flip-flop 9, is arranged so as to respond to this state "0" of the output Q of the flip-flop 9 by disconnecting the motor coil M from the source d power supply and by putting this coil in short circuit.

From time tt, the voltage U _m across the motor coil M is therefore zero, and the current i _m begins to decrease. When it becomes lower than the current l _ref , the output 7a of the comparator 7 returns to the state "1". At the next sampling instant, the output Q of flip-flop 9 therefore also goes to state "1". In response to this latter state "1", the circuit 1 eliminates the short-circuit of the coil of the motor M and reconnects this coil to the power source. The current i _m therefore begins to increase again, and the process described above starts again until an instant designated by t _n in FIG. 2, where the circuit 1 receives on an input 1c a signal to interrupt the driving pulse. .

This interrupt signal consists of the transition from logic state "0" to logic state "1" "of the output of a circuit which will be described below, an output which is of course connected to this input 1 of the trainer 1.

In response to this interrupt signal, circuit 1 disconnects the motor coil M from the power source and short-circuits this coil permanently, until the next instant to where the whole process described above starts again.

It should be noted that, in reality, your period Δ of the sampling signal is short compared to the rise or fall times of the current in the coil. It follows that the amplitude of the exceedances of i _m on either side of l _ref is low, and that we can consider that i _m is constant and equal to l _ref between the instants t ₁ and t _n . It also results therefrom that the periods of the sampling signal are much more numerous than that which has been represented in FIG. 2 during each of the periods when the current in the coil increases or decreases.

For each time t _x located after time t ₁ where the current i _m is interrupted for the first time, the terms of equation (2) above can be written:

At time t ₁ , the rotor has practically not yet rotated, and the motor has not yet provided any mechanical energy. So we have

• Eme_0x ⁼ Eme _1x ⁼ Ep_1x -Ej_1x -Ema_1x (7)

Taking this fact into account, we can easily see that equation (2) above can be written:

• Eme _0x ⁼ Eme _1x ⁼ Ep _1x -Ej _1x -Ema _1x (7)

dans lesquelles les symboles ont la même signification que dans les équations (3), (4) et (5).Analogously to what was done above for the terms of equation (2), we can write the terms of equation (7) as follows:

in which the symbols have the same meaning as in equations (3), (4) and (5).

dans laquelle i_m(x) et i_m(1) sont respectivement les courants circulant dans la bobine aux instants t_x et t₁.From equation (5 ') above, it is easy to draw that

in which i _m (x) and i _m (1) are the currents flowing in the coil respectively at times t _x and t ₁ .

But, as we saw above, the current i _m is practically constant and equal to l _ref between the instants t ₁ and t _n . If the instant t _x considered is located before this instant t _n , we see that i _m (x) = i _m (1), and that Ema _1x = O.

ou encore

Equation (7) above can therefore be written, in this particular case,

or

During each driving pulse, the motor coil is connected to the power source for a certain number of periods of the sampling signal each having a duration A. In the following description, we will call C1 _x the number of these periods which are between the instant t ₁ when the current in the coil is interrupted for the first time and the instant t _x considered.

During each of these C _1x periods, the current i _s supplied by the source is equal to the current i _m flowing in the coil, which is itself practically equal to the reference current I _ref .

During the other periods of the sampling signal located between time t ₁ and time t _x , the motor coil is disconnected from the power source. The current i _s is therefore zero during these other periods.

It follows that we can write:

Furthermore, if we call C2 _x the total number of periods of the sampling signal located between instants t1 and t _x , we see that

ou encore:

avec

et

Equation (8) above can therefore be written:

or:

with

and

The factors k and p being constant, it follows from equation (10) that, in the present case where the current flowing in the coil is practically constant and equal to 1 ref, the quantity of electrical energy Eme _0x converted into mechanical energy by the motor between the start of a driving impulse and any instant t _x is proportional to the difference between, on the one hand, the product of the number C1 _x by the factor p and, on the other hand, the number C2 _x .

avec

et

comme dans l'équation (10).Note that equation (9) above can also be written:

with

and

as in equation (10).

Consequently, the quantity of energy Eme _ox is also proportional to the difference between, on the one hand, the number C1 _x and, on the other hand, the quotient of the number C2 _x by the factor p.

For the value of Eme _ox given by one or the other of equations (10) or (11) above to be exact, it is obviously necessary that the instant t _x considered is not absolutely arbitrary, but that it coincides with one of the sampling instants. However, since the frequency of the sampling signal is relatively high, the error made when the instant t _x considered does not coincide with a sampling instant is small.

In cases where the factor p which multiplies the number C1 _x in equation (10) above is an integer, the calculation of the term in parentheses in this equation (10) can be done quite simply. It can be seen that it is sufficient for example to increment a reversible counter by p units during each of the periods of the sampling signal where the motor coil is connected to the power source, and to decrement this counter by one unit at every sampling instant, whether the coil is connected to the power source or not. The content N _x of this counter will thus be permanently equal to p.C1 _x -C2 _x , and therefore proportional to the quantity of energy Eme _ox .

At the sampling times when the coil is connected to the power source, the counter must be incremented by p units and, simultaneously, decremented by one unit. To avoid the problems which may arise due to this simultaneity, one can simply increment the counter by (p-1) units at each sampling instant when the motor coil is connected to the power source, and does not decrement this counter by one unit only at the sampling times when the motor coil is disconnected from the power source.

Under these conditions, the content N _x of the counter is permanently equal to

We can easily see that this expression (12) is equal to the term in parenthesis of equation (10) above.

The same principle can be used in cases where the factor p mentioned above is not an integer.

In these cases, it is sufficient for example to increment the counter by n. (P-1) units during the periods of the sampling signal where the motor coil is connected to the power source, n being an integer such that n. (p-1) is also an integer, and to decrement the counter by n units when the motor coil is disconnected from the source. Under these conditions, the content of the counter is permanently equal to

On voit facilement que cette expression (13) est égale à n fois le terme entre parenthèses de l'équation (10) ci-dessus et qu'elle est donc également proportionnelle à la quantité d'énergie Eme_0x.

We can easily see that this expression (13) is equal to n times the term in parentheses of equation (10) above and that it is therefore also proportional to the amount of energy Eme _0x .

FIG. 1 also shows the diagram of an example of a circuit making it possible to calculate expression (12), in a case where the factor p defined above is equal to 4. In this case, the reversible counter mentioned above must therefore be incremented by three units at each sampling instant when the motor coil is connected to the power source, and decremented by one unit at each sampling instant when this coil is disconnected from this source and activated short circuit.

This reversible counter is designated by the reference 8 in FIG. 1. Its clock input 8a is connected to the output of a logic circuit formed by AND gates 11 to 13 and OR gates 14 and 15, which are linked together , with the outputs Q and Q of the flip-flop 9, with the output of the oscillator 3 and with the outputs 2c and 2d of the frequency divider 2 as shown.

The input 8b for controlling the counting direction of this counter 8 is connected to the output Q of the flip-flop 9, and its reset input 8c is connected to the output Q of a rocker 10 of type D.

The clock input CL of this flip-flop 10 is connected to the output Q of the flip-flop 9, its input D is permanently connected to the potential corresponding to the logic state "1", and its reset input R is connected to the output of the circuit, already mentioned, which produces the signal to interrupt the driving pulse in the form of a transition from logic state "O" to logic state "1" and which will be described later .

At the end of each driving pulse, the output Q of the flip-flop 10 is therefore set to the state "1". It is easy to see that this exit Q of flip-flop 10 is still in this state "1""at time to which marks the start of the next driving pulse, and that it remains in this state until time t ₁ following this time to.

Between the end of a driving pulse and the instant t ₁ situated after the beginning of the following driving pulse, the reset input R of counter 8 is therefore in state "1", and the content of this counter is zero.

It should be noted that, in general, the content of counter 8 is a number which is represented in a binary system by the states "O" or "1" of the outputs 8d to 81 of this counter 8. The weight figure the the lowest of this number is represented by the logic state of the output 8d, and the most significant digit is represented by the state of the output 81.

We have seen above that, after each instant to, the output Q of flip-flop 9 goes to state "O" at instant t ₁ which is the sampling instant following the instant when the current i _m exceeds for the first time the reference current I _ref .

At this instant t ₁ , the output Q of the flip-flop 10 therefore passes to the state "0" in response to this transition to the state "O" of the output Q of the flip-flop 9.

It is easy to see, using the diagrams of FIG. 6, that during each period of the sampling signal, the output 15a of the gate 15 delivers three pulses when the output Q of the flip-flop 10 is in the state "1", or a single pulse when this output Q of flip-flop 10 is in the state "O".

As long as the reset input R of counter 8 is in state "1", these pulses produced by the output 15a of gate 15 have no effect on counter 8, the content of which is kept at zero .

On the other hand, from the instant t ₁ , these pulses increment or decrement this counter 8, according to the state of its input 8b.

It is easy to see that, when the output Q of the flip-flop 9 is in the state "1", that is to say when the coil of the motor M is connected to the power source, the counter 8 is incremented by one by each of the three pulses produced by the output 15a of gate 15 during each period of the sampling signal.

Similarly, the counter 8 is decremented by one unit at each period of the sampling signal when the output Q of the flip-flop 9 is in the "O" state, that is to say when the coil of the motor M is disconnected from the power source and short-circuited.

We therefore see that, at any instant t _x located after an instant t ₁ and until the end of each driving pulse, the content of counter 8 is equal to the number N _x defined by expression (12) above , and that it is therefore proportional to the quantity of electrical energy Eme _ox which has been converted into mechanical energy by the motor since the start of the driving pulse.

The calculation of the amount of energy Eme _ox can also be done on the basis of equation (11) above, using a reversible counter whose content is at all times a number N ' _x equal at the end of this equation (11) in parentheses.

In this case, this counter is for example incremented by one unit at each sampling instant when the coil is connected to the power source, and permanently decremented at a frequency equal to the ratio between the frequency of the sampling signal and the factor p.

FIG. 7 represents an example of the modifications that can be made to the circuit of FIG. 1 to make it a circuit for measuring the quantity of energy Eme _ox using the equation (11) above, in a case where the frequency of the sampling signal is 8,192 Hz as in the example in FIG. 1, and the factor p is equal to 2.67. The frequency of the counter decrementing signal mentioned above is therefore, theoretically, equal to 3'068.2 Hz.

The components 1 to 7 of this circuit are identical to the components of the circuit of FIG. 1 which bear the same references and have not been shown in this FIG. 7. The flip-flops 9 and 10 of this FIG. 7 are identical to those which bear the same references in Figure 1 and are ordered in the same manner as the latter.

The counter 8 in FIG. 1 is replaced by a reversible counter 27 having an increment input 27a, a decrement input 27b and a reset input 27c.

The increment input 27a of the counter 27 is connected to the output of an AND gate 30 whose inputs are respectively connected to the output Q of the flip-flop 9 and to the output 2d of the divider 2, which is the output which delivers the sampling signal.

The decrementing input 27b of the counter 27 is connected to the output of an AND gate 28 whose inputs are respectively connected to the output 2e of the divider 2 and to the output of a NAND gate 29. The inputs of this gate 29 are respectively connected to outputs 2f and 2g of divider 2.

The reset input 27c of the counter 27 is connected to the output Q of the flip-flop 10.

It can be seen that, as is the case for the counter 8 in FIG. 1, the content of the counter 27 is kept at zero from the end of each driving pulse until the instant ti which follows the start of the pulse. next motor.

From this instant ti, the content of the counter 27 is incremented by one unit at each sampling instant where the output Q of the flip-flop 10 is in the state "1", that is to say where the coil of the motor M is connected to the power source.

Furthermore, still from this instant ti, the content of the counter 27 is decremented by the signal produced by the output of the gate 28.

It is easy to see, using the diagrams in FIG. 8, that this decrementing signal of the counter 27 has an average frequency equal to three-quarters of the frequency of the signal supplied by the output 2e of the divider 2, ie 3'072 Hz.

It can therefore be seen that, from each instant ti, the content of the counter 27 is a number which is practically permanently equal to the number N x defined above, and therefore to the term in parentheses of equation (11) ci- above, and that it is therefore also practically proportional to the amount of energy Eme _0x .

The fact that the average frequency of the decrementing signal of the counter 27 is equal, in this case, to 3.072 Hz and not to the theoretical value of 3.068.2 Hz obviously introduces an error in this calculation of the quantity of Eme _oX energy. In this particular case, this error is small enough to be able to be neglected.

It is not always easy to produce from the signals available in the circuit a decrementing signal from the counter 27 having a frequency close enough to the theoretical frequency so that the error made on the measurement of the quantity of energy Eme _ox is negligible. In such a case, it suffices to modify the value of the current I _ref which has been chosen, so that the coefficient p takes a value for which the theoretical frequency of the decrementing signal of the counter 27 is equal, or at least almost equal, at the frequency of a signal which can be easily produced from the available signals.

We have seen above that, for each value of the resistive torque Tr which opposes the rotation of the rotor during a driving pulse, the motor must supply a determined quantity of mechanical energy Emm so that its rotor takes just one step in response to this driving impulse. So that the consumption of the motor is minimal, it is therefore necessary to interrupt each driving pulse at the moment when the quantity of electrical energy Eme converted into mechanical energy by the motor reaches this value Emm.

We have also seen above that, during each driving pulse, the time T taken by the quantity of energy Eme to reach the value of a quantity of reference energy E _ref predetermined depends on the resisting torque Tr which is opposed to the rotation of the rotor, and that there is a well-defined relationship between this time T and the optimal duration _T of the driving pulse.

FIG. 5 gives an example of this relationship which obviously depends on the characteristics of the engine and of the mobile elements which it drives and which can be determined analytically and / or by tests.

To determine the optimal duration T of a motor pulse, it is therefore necessary to permanently measure the quantity of electrical energy Eme converted into mechanical energy since the start of this motor pulse, measure the duration T of the time period which separates the start of the driving pulse of the instant, designated by tz, when this quantity of energy Eme reaches the value of the quantity of reference energy E _ref , determine the optimal duration τ of the driving pulse corresponding to this duration T, and interrupt the motor pulse when its duration becomes equal to this optimal duration r.

We have seen above that, in fact, the circuit for measuring the amount of energy Eme, examples of which have been described, does not give the real value of this amount of energy Eme, but provides a measurement signal , analog or digital, which is proportional to it. In practice, the duration T mentioned above is therefore that which separates the start of the driving pulse from the instant when this measurement signal reaches a reference value proportional to the quantity of reference energy E _ref . The proportionality relationships between the quantity of energy Eme and the value of the measurement signal on the one hand, and between the quantity of reference energy E _ref and the reference value on the other hand are of course equal.

In the present example, where the consumption of the motor must be as low as possible, the quantity of reference energy E _{ref is} preferably chosen as the quantity of energy Emm _min that the motor must supply so that its rotor takes just one step when the resisting torque which it must overcome has its minimum value Trmin.

One could also choose for E, _ef a value lower than that of the quantity of energy Emm _min . On the other hand, it would not be wise to choose for E _ref a value greater than that of the quantity of energy Emm _min , because the duration of the driving pulses would then be greater than the optimal duration each time that the resisting torque Tr would have its value minimum Tr _min .

The instant t ₂ defined above is therefore that when the measurement signal produced by the circuit for measuring the quantity of energy Eme reaches the value corresponding to this quantity of energy Emm _min .

FIG. 1 also represents an example of a circuit making it possible to measure the duration T which separates the start of a driving pulse from this instant t ₂ .

It may be recalled that, in this FIG. 1, the signal for measuring the quantity of electrical energy Eme converted into mechanical energy by the motor since the start of a driving pulse consists of the content of the counter 8, that is ie by the binary number formed by the logical states "O" or "1" of the outputs of this counter 8.

In the example of this FIG. 1, the value of the measurement signal corresponding to the energy Emm _min taken as reference is that for which the outputs g, h, k and 1 of the counter 8 are simultaneously in the logic state "1 ", the other outputs of this counter 8 being in the logic" O "state. The binary number represented by this combination of states has a value, expressed in decimal notation, of 408.

The circuit for measuring the duration T comprises a NAND gate 19 whose inputs are each connected to one of the outputs g, h, k and 1 of the counter 8.

The output of this gate 19 is connected to the clock input CL of a flip-flop 20, of type D, whose input D is permanently connected to the potential representing the logic state "1" and whose input Reset zero is connected to the output Q of scale 10.

The output Q of this flip-flop 20 is connected to the control input CL of a memory circuit 22, the inputs of which are connected to the outputs d to k of the divider 2.

The memory circuit 22 is of a well known type. It is arranged so that, when its control input CL is in the state "O", it is "transparent", that is to say that the logic state of its outputs i to p is identical, in permanence, in the logical state of its inputs a to h. On the other hand, when its control input CL is in state "1", its outputs i to p are blocked in the logic state that they had at the time when this input CL took this state "1".

• On a vu ci-dessus que, entre la fin d'une impulsion motrice et l'instant t₁ situé après le début de l'impulsion motrice suivante, la sortie Q de la bascule 10 est à l'état "1". Pendant ce temps, la sortie Q de la bascule 20 est donc maintenue à l'état "O", et le circuit de mémoire 22 est transparent. En outre, le contenu du compteur 8 est maintenu à zéro.

The time measurement circuit T formed by the gate 19, the flip-flop 20 and the memory circuit 22 operates as follows:

• We have seen above that, between the end of a driving pulse and the instant t ₁ located after the start of the next driving pulse, the output Q of flip-flop 10 is in state "1". During this time, the output Q of the flip-flop 20 is therefore maintained in the "O" state, and the memory circuit 22 is transparent. In addition, the content of counter 8 is kept at zero.

At the instant t _o which marks the start of each driving pulse, all the outputs of the divider 2 are in the logic state "O". After this instant to the states of these outputs change regularly, at the rate of the signal produced by the oscillator 3, and these logical states together form a binary number which represents, at each instant, the duration which has elapsed since the instant to immediately preceding.

At time t ₁ following the start of a driving pulse, the output Q of the flip-flop 10 goes to state "O", and the content of the counter 8 begins to increase, so as to represent the amount of electrical energy Eme converted into mechanical energy by the motor.

When, at the instant t ₂ , this content of the counter 8 reaches the reference value mentioned above, in the present example the value 408, the output of the gate 19 goes to the state "" O ". In response to this passage, the Q output of flip-flop 20 goes to state "1". From this instant t ₂ , the outputs of the memory circuit 22 therefore remain blocked in a state which is that which the outputs d to k of the divider 2 had at this instant t ₂ . The binary number formed by the logic states of the outputs i to p of the memory circuit 22 is therefore a measure of the duration T of the period of time which has elapsed between the start of the driving pulse and the instant t ₂ where the quantity of energy Eme has reached the predetermined reference value, in this example the value Emm _min .

It should be noted that gate 19 plays the role of a digital comparator, since it produces a signal when the content of counter 8 becomes equal to the reference number, in this example 408. It could therefore be replaced without difficulty by such a digital comparator, the first inputs of which would be connected to the outputs 8d to 8m from counter 8, and the second inputs of which would be permanently connected to the potentials representing the logical states "0" or "1" so that the combination of these states forms the number binary wanted.

FIG. 1 also shows an example of a circuit intended to determine the optimal duration τ of the driving pulse as a function of the duration T measured by the circuit described above. In this example, this circuit includes a simple read only memory 23, often called PROM, a word formed by the initials of its designation in English (Programmable Read Only Memory).

The inputs a to h of this read only memory 23 are connected to the outputs i to p of the memory circuit 22, and it is programmed so as to materialize the relationship between the time T measured by the circuit which has just been described and the duration optimal r of the motor impulse. This means that for each binary number formed, after each instant t ₂ , by the logic states of the outputs i to p of the memory circuit 22, that is to say for each particular value of the time T, the outputs i to p of the read only memory 23 have logical states forming a second binary number which represents the optimal duration τ corresponding to this time T.

FIG. 1 also shows an example of a circuit making it possible to interrupt the driving pulse when its duration becomes equal to the optimal duration τ determined using the read only memory 23.

This circuit comprises, in this example, a digital comparator 24 whose first inputs a to h are connected to the outputs d to k of the divider 2, and whose second inputs a 'to h' are connected to the outputs i to p of the memory dead 23. The output s of comparator 24 is normally in logic state "0", and it takes state "1" only if the binary number formed by the logic states of its inputs a to h is equal to the number binary formed by the logical states of its inputs a 'to h'.

This output s of the comparator 24 is connected to a first input of an AND gate 25, the second input of which is connected to the output Q of the flip-flop 20 via a delay circuit 26 whose role will be described later. The output 25a of the gate 25 is connected to the input 1 of the formatter circuit 1 and to the input R for resetting the flip-flop 10 to zero.

We have seen above that, during each driving pulse, the outputs i to p of the read-only memory 23 present, after time t ₂ , logical states which form a binary number corresponding to the optimal duration r of this driving pulse . After this instant t ₂ , the binary number formed by the logic states of the outputs d to k of the divider 2 continues to increase. When this binary number becomes equal to that which is formed by the logical states of the outputs i to p of the read only memory 23, that is to say at the instant t _n when the duration of the driving pulse becomes equal to the optimal duration _T , the output s of comparator 24 goes to state "1". The output of the delay circuit 26 also being in the state "1" at this time, the output 25a of the gate 25, and therefore the input 1c c of the formatter circuit 1 and the input R of resetting to zero flip-flop 10, also change to state "1".

Consequently, the forming circuit 1 interrupts the driving pulse, and the content of the counter 8 is reset to zero.

This situation remains unchanged until the next instant, when the whole process described above begins again.

It may happen that, just after time t ₂ , the outputs i to p of the read-only memory 23 take, for a very short time, a logic state different from their final state. The delay circuit 26, which in the present example comprises two inverters and a capacitor connected in the manner shown, is intended to prevent a state "1" which may appear at the output s of the comparator 24 during this time from causing the premature interruption of the motor impulse.

In summary, it can be seen that each driving pulse produced by the circuit of FIG. 1 has a duration which is equal to the optimal duration _T corresponding to the resistive torque Tr which is effectively applied to the rotor during this driving pulse.

All other things being equal, the method according to the invention implemented by the circuit of FIG. 1, for example, is therefore that which makes it possible to control the motor with the lowest electrical energy consumption.

This advantage is due to the fact that the physical quantity which is the basis for determining the duration of each driving pulse is the quantity of electrical energy converted into mechanical energy by the motor, the variation of which as a function of time is directly linked to the value of the resistive torque which the motor rotor must overcome during this driving impulse.

In the cases where, as in the case of FIG. 1, the motor is controlled so that the current i _m passing through its coil during a driving pulse is substantially constant and equal a value I _ref between the instants t ₁ and t _n , the total amount of electrical energy Ep supplied by the power source during this driving pulse obviously depends on this value I _ref .

Figure 3 shows an example of the shape of this dependence for four different resistant couples Tr _min , Tr1, Tr2 and Tr _max .

It can be seen in this FIG. 3 that, for each value of the resistive torque, there is a value 1 _ref for which this quantity of energy Ep is minimal.

FIG. 3 also shows that this value I _ref for which the amount of energy Ep is minimum increases with the value of the resistive torque Tr.

In addition, it can be seen in this FIG. 3 that if the value I _min is chosen for I _rel corresponding to the minimum quantity of energy Ep that the motor power source must supply when the resistive torque Tr has its value Tr _min , this amount of energy Ep increases very rapidly with the increase in the resistive torque Tr. This amount of energy Ep can even become infinite when the resistive torque Tr approaches its maximum value Trmax. This means that the motor is no longer able, in this case, to convert enough electrical energy into mechanical energy to turn the rotor or, in other words, that the optimal duration _T of the driving pulse should be infinite, as shown in Figure 4.

It is therefore judicious to choose for the reference current I _ref a value greater than the value I _min mentioned above and less than or equal to the value I _max which is the one for which the quantity of energy Ep is minimum when the torque resistant Tr has its maximum value Tr _max . This value I _ref is preferably chosen so that, whatever the resistive torque Tr, the quantity of energy Ep actually supplied by the source is only slightly greater than the minimum quantity of energy Ep corresponding to this couple Tr. The value indicated in figure 3 fulfills this condition.

Considerations similar to the previous ones can be made in cases where the motor is controlled so that the voltage applied to it is constant during each driving pulse, i.e. in such a case there is a value optimum of this voltage for which the quantity of energy Ep supplied by the power source is minimal.

However, this power source generally consists of a battery, the voltage of which cannot be freely chosen.

It would therefore be necessary to provide a circuit producing this optimal voltage from the voltage of the power source. However, such a circuit itself consumes a significant amount of electrical energy. It follows that, overall, the consumption of a motor supplied by this optimum voltage is not significantly lower than the consumption of the same motor supplied directly by the voltage of the power source.

In the examples described above, the measurement of the amount of electrical energy Eme converted into mechanical energy by the motor during a driving pulse is used to determine the duration of this driving pulse.

This measurement can also be used to determine whether or not the rotor turns correctly in response to this driving impulse.

We have seen above that the time T taken by the quantity of energy Eme to reach the reference value E _ref is a measure of the value of the resistive torque Tr applied to the rotor. When this torque Tr has its maximum value Tr _max , this time T therefore also has a maximum value T _max , which of course depends on the characteristics of the motor and the load it drives.

It follows that if, for any reason, the resistive torque Tr applied to the rotor during a driving pulse has a value greater than its maximum value Tr _max , the quantity of energy Eme does not reach the reference value E _ref before that the time T _{max has} not elapsed.

It is the same if, always for whatever reason, the polarity of the driving pulse does not correspond to the angular position occupied by the rotor at the start of this driving pulse, and that, consequently, the latter cannot rotate this rotor, regardless of the value of the resisting torque Tr.

It is therefore possible to detect whether the rotor turns correctly or not in response to a driving pulse by determining at a detection instant t _d separated from the start of this driving pulse by a duration at least equal to T _max if the amount of energy Eme has reached the reference value or not.

FIG. 9 shows the diagram of an example of a circuit which performs this detection in a case where the time T _max has a duration of approximately 11 milliseconds.

This circuit comprises in this case a flip-flop 41 of type D and an AND gate 42.

The clock input CL of the flip-flop 41 is connected to the output 2a of the divider 2 of FIG. 1, its input D is permanently connected to the potential which represents the logic state "1", and its input R of reset at zero is connected to the output Q of the flip-flop 20 of FIG. 1. The inputs of the gate 42 are respectively connected to the output Q of this flip-flop 41 and to the outputs 2j and 2k of the divider 2 of FIG. 1.

It is easily seen with the aid of the diagrams of Figures ₁ 0a and 10b, the Q output of flip-flop 41 goes to state "1" at each time t _o. Furthermore, it can be seen that, after each instant t ₀ , at least one of the outputs 2j and 2k of the divider 2 is in the state "0" for a period and a half of the signal produced by the output 2j of the divider 2, or for 11.7 milliseconds. In this example, the instant situated at the end of this 11.7 millisecond period when the 128 Hz signal produced by the output 2j of the divider 2 goes to state "1" is the detection instant t _d mentioned above. The output 42a of the gate 42 is therefore maintained in the state "O" until this instant td, independently of the state of the output Q of the flip-flop 41.

If the motor rotor turns correctly in response to a driving pulse starting at an instant t _o , the quantity of energy Eme reaches the reference value E _ref at an instant t ₂ located less than 11 milliseconds after this instant t ₀ , c that is to say before time t _d . At this time t ₂ , the Q output of flip-flop 20 goes to state "1", as has been shown above, and the Q output of flip-flop 41 therefore returns to state "0" and y remains until the start of the next motor pulse. The output 42a of door 42 therefore also remains in the "O" state. This situation is illustrated in Figure 10a.

If, on the other hand, the rotor does not rotate correctly in response to a driving pulse, the amount of energy Eme has not yet reached the reference value E _ref at time t _d . The Q output of flip-flop 20 is therefore still in the "O" state, and the Q output of flip-flop 41 is still in the "1" state. As a result, the output 42a of the door 42 changes to the state "1" at this instant t _d . This state "1" constitutes the detection signal of the non-rotation of the rotor. This situation is illustrated in Figure 1 Ob.

A circuit such as that shown in FIG. 9 is obviously particularly well suited for detecting the rotation or non-rotation of the rotor of a motor controlled by driving pulses, the duration of which is adjusted as a function of the amount of energy. electrical Eme converted into mechanical energy during these driving pulses, since the means for measuring this quantity of Eme energy are already included in the circuit producing these driving pulses.

It should however be noted that this detection of the rotation or of the non-rotation of the rotor can also be carried out whatever the way in which these driving pulses are produced.

Thus, it is for example entirely possible to design a control circuit for a stepping motor comprising a trainer producing driving pulses having a first fixed duration, relatively short, or a second duration, longer than the first, according to whether a detection signal indicates that the rotor turns correctly or not in response to short-term driving pulses.

This detection signal could be produced by a circuit comprising means for measuring the quantity of energy Eme such as those formed by the elements 5 to 15 of FIG. 1, means for determining the instant when this quantity energy Eme reaches a reference value E _ref such as those formed by the elements 19 and 20 of this figure 1, and means for detecting the rotation or non-rotation of the rotor such as those formed by elements 41 and 42 of FIG. 9.

The measurement of the quantity of energy Eme can also be used in a circuit producing driving pulses during which the quantity of mechanical energy supplied by the motor has a fixed and predetermined value.

Such a circuit will not be shown here, because it can be very similar to that of FIG. 1. It suffices in fact to replace therein the door 19 by a door of the same kind but whose inputs are connected to the outputs of the counter 8 which are in state "1" when the amount of energy Eme is equal to this amount of mechanical energy of predetermined value. In addition, the elements 22 to 26 of the circuit of FIG. 1 can be deleted, the output Q of the flip-flop 20 then being directly connected to the input 1 of the forming circuit 1.

It is easy to see that, with such a circuit, each driving pulse is interrupted as soon as the quantity of energy Eme becomes equal to the predetermined value. The amount of mechanical energy supplied by the motor during these motor pulses is therefore constant.

These latter driving pulses can advantageously replace the fixed-duration catch-up pulses which are produced by certain known control circuits when the motor rotor does not rotate correctly in response to one of the short pulses which they normally produce.

In such a case, the predetermined value mentioned above is obviously preferably that of the quantity of mechanical energy Emm _max that the motor must supply when the resistive torque Tr applied to its rotor has its maximum value Tr _max .

The fact that the quantity of mechanical energy Emm supplied by the motor during these pulses has a fixed value has the advantage that they never cause the rotor to rotate by more than one step, unlike what can happen with fixed-duration catch-up pulses produced by known control circuits.

A circuit combining in the manner mentioned above the production of motor pulses of fixed and relatively short duration and the production of make-up pulses during which the amount of mechanical energy supplied by the motor is constant and predetermined will not be described here because its realization is within the reach of the skilled person.

It should also be noted that the present invention is not limited to the control of stepping motors as they are commonly used in electronic timepieces, that is to say which comprise a rotor comprising a magnet. bipolar permanent disposed in a substantially cylindrical opening formed in a stator carrying a coil, but that it can be used to control stepping motors of any kind, for example motors whose rotor comprises a permanent multipolar magnet and / or whose stator carries two or more coils.

Claims (17)

1. A method of controlling a stepping motor (M) comprising a coil and a rotor magnetically coupled to said coil, said method comprising applying to said coil a driving pulse each time said rotor has to rotate a step, characterized by the fact that it further comprises the measurement of the amount of electrical energy (Eme} converted into mechanical energy by the motor since the start of said driving pulse, the comparison between said amount of electrical energy ( Eme) and an energy reference value (E _ref ) and the interruption of said motor pulse depending on said comparison. 2. Method according to claim 1, characterized in that said energy reference value (E _ref ) is substantially equal to the amount of mechanical energy (Emm _min ) that said motor (M) must supply so that said rotor just turns one step when the resistive torque (Tr) applied to it has its minimum value (Tr min), and when said interruption involves the measurement of the time (T) taken by said quantity of electrical energy to reach said value of energy reference (E _ret ) and the determination of the optimal duration ( _T ) of the driving pulse as a function of said time (T), said driving pulse being interrupted at the end of said optimal duration ( _T ). 3. Method according to claim 1, characterized in that said energy reference value (E _ref ) is substantially equal to the amount of mechanical energy (Emm _max ) that said motor (M) must provide for said rotor just turns one step when the resistive torque (Tr) applied to it has its maximum value (Tr _max ), and that said interruption is performed in response to said comparison when said quantity of electrical energy (Eme) reaches said value energy reference (E _ref ). 4. Method according to claim 1, characterized in that it further comprises the production of a detection signal of the non-rotation of said rotor when said quantity of electrical energy (Eme) does not reach said value of energy reference (E _ref ) after a determined time. 5. Method according to claim 1, characterized in that said measurement of said quantity of electrical energy (Eme) comprises the calculation of the following first expression:

in which: -to and t _x are respectively the instant of start of the driving impulse and any instant situated after the instant to; -Eme _0x is said quantity of electrical energy (Eme) converted into mechanical energy between instants to and tx; -U is the voltage of the motor power source (M); -i _s (t) is the current supplied by this power source; -i _m (t) is the current flowing in the motor coil (M); and -R and L are respectively the resistance and the inductance of this coil. 6. Method according to claim 5, characterized in that it further comprises the production of a periodic sampling signal defining a plurality of sampling instants, two consecutive sampling instants being separated by an equal period at the period of said sampling signal, the control of the current (i _m ) flowing in said coil during said driving pulse to a current reference value (I _ref ) comprising the connection of said coil to said source at each instant d sampling where said current (i _m ) flowing in said coil is less than said current reference value (I _ref ) and the disconnection of said coil from said source and the short-circuiting of said coil at each instant of sampling where said circulating current (i _m ) is greater than said current reference value (I _ref ), said first expression then being reduced to the following second expression:

in which: -Δ is the duration of the period of said sampling signal. -C1 _x is a first number equal to the number of sampling instants where said current (i _m ) flowing in said coil is greater than said current reference value (I _ref ) which are located between instant t ₀ and the instant t _x ; and -C2 _x is a second number equal to the total number of sampling instants located between instant to and instant t _x 7. Method according to claim 6, characterized in that the calculation of said second expression comprises the calculation of a third number (N _x ) according to the following formula:

in which: -I _x is said third number; and -p is a constant factor equal to

said third number (NJ being proportional to said amount of Emeox energy. 8. Method according to claim 6, characterized in that the calculation of said second expression comprises the calculation of a third number (N x) according to the following formula:

in which: -N ' _x is said third number; and -p is a constant factor equal to

said third number (N x) being proportional to said quantity of energy Eme _ox . 9. Device for implementing the method according to claim 1, comprising means (1) for producing said motor pulse, characterized in that it also comprises means (8, 10 to 15; 10, 27 to 30) for producing a signal for measuring the amount of electrical energy (Eme) converted into mechanical energy by said motor since the start of said driving pulse, means (19) responding to said measurement signal to produce a comparison signal between said quantity of electrical energy (Eme) and an energy reference value (E _ref ), and means (20, 22 to 25; 20) for producing an interruption signal of said driving pulse in dependence on said signal comparison. 10. Device according to claim 9, characterized in that the said quantity of reference energy (E _ref ) is substantially equal to the quantity of mechanical energy (Emm _min ) that the said motor must supply so that the said rotor turns just d 'a step in response to said driving pulse when the resistive torque (Tr) applied to said rotor has its minimum value (Tr _min ), and when said means (20, 22 to 25; 20) for producing an interrupt signal include means (20, 22) for measuring the time (T) taken by said electrical energy (Eme) to reach said energy reference value (E _ref ), means (23) for determining the optimal duration ( _T ) of said driving pulse as a function of said time (T), and means (24, 25) for producing said interruption signal at the end of said optimal duration ( _T ). 11. Device according to claim 9, characterized in that said energy reference value (E _ref ) is substantially equal to the amount of mechanical energy (Emm _max ) that said motor must supply so that said rotor turns just d 'a step in response to said driving pulse when the resistive torque (Tr) applied to said rotor has its maximum value (Tr _max ), and by the fact that said means (20, 22 to 25; 20) for producing a signal of interrupt include means (20) for producing said interrupt signal in response to said comparison signal. 12. Device according to claim 9, characterized in that it further comprises means (41, 42) for producing a detection signal of the non-rotation of said rotor when said quantity of electrical energy (Eme) does not not reach said energy reference value (E _ref ) after a determined time. 13. Device according to claim 9, characterized in that said means (8, 10 to 15; 10, 27 to 30) to produce a signal for measuring said quantity of electrical energy (Eme) are arranged so as to calculate the following first expression:

in which: -to and t _x are respectively the instant of start of the driving impulse and any instant situated after the instant to; -Eme _ox is said quantity of electrical energy (Eme) converted into mechanical energy between instants to and t _x ; -U is the voltage of the motor power source (M); -i _s (t) is the current supplied by this power source; -i _m (t) is the current flowing in the motor coil (M); and -R and L are respectively the resistance and the inductance of this coil. 14. Device according to claim 13, characterized in that said means (1) for producing a driving pulse are arranged so as to respond, during said driving pulse, to a first state of a control signal to connect said source d supply to said coil and to a second state of said control signal to disconnect said source from said coil and to short-circuit said coil, in that it further comprises means (2d) for producing a signal d periodic sampling defining a plurality of sampling instants separated from each other by periods equal to the period of said sampling signal, means (5 to 7, 9) responding to said sampling signal to produce said sampling signal control with said first or said second state depending on whether, at one of said sampling instants, the current (i _m ) flowing in said coil is less than or greater than a current reference value ( I _ref ), said current (i _m ) being thus subject to said current reference value (I _ref ) and said first expression then being reduced to the following second expression:

in which: -Δ is the duration of the period of said sampling signal. -C1 _x is a first number equal to the number of sampling instants where said current (i _m ) flowing in said coil is greater than said current reference value (I _ref ) which are located between instant to and l 'instant t _x ; and -C2 _x is a second number equal to the total number of sampling instants located between instant to and instant t _x . 15. Device according to claim 14, characterized in that said means (8, 10 to 15; 10, 27 to 30) for producing a signal for measuring said quantity of electrical energy (Eme) comprise means (11 to 15) responding to said sampling signal and said control signal to produce (p-1) increment pulses, with

at each sampling instant when said control signal is in its first state and for producing a decrementing pulse at each sampling instant when said control signal is in its second state, and counting means (8) responding to said increment pulses and said decrement pulses to produce said signal for measuring said amount of electrical energy (Eme). 16. Device according to claim 14, characterized in that the said means (8, 10 to 15; 10, 27 to 30) for producing a signal for measuring the said quantity of electrical energy (Eme) comprise means (28 to 30) responding to said sampling signal and said control signal to produce an increment pulse at each sampling instant when said control signal is in its first state and to produce periodic decrement pulses having a period equal to p times the period of said sampling signal, with

and counting means (27) responding to said increment pulses and said decrement pulses to produce said signal for measuring said amount of electrical energy (Eme).

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