CH680253B5 - - Google Patents

Abstract

Bidirectional stepping motor has two coils applying magnetic fields whose vector sum achieves required torque on motor

Description

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Description

The present invention relates to a stepping motor with two directions of rotation comprising:

- a rotor comprising a permanent magnet producing a first magnetic field;

- A first coil crossed by a first part of said first magnetic field and intended to produce a second magnetic field in response to a first current;

- A second coil crossed by a second part of said first magnetic field and intended to produce a third magnetic field at a second current, said first and second parts of said first magnetic field forming in the permanent magnet a first resulting field;

- first means for applying said second magnetic field to said permanent magnet in a first direction;

- second means for applying said third magnetic field to said permanent magnet in a second direction symmetrical to the first direction with respect to an axis of symmetry; and

- Positioning means intended to maintain or bring said rotor into one or the other of a plurality of rest positions.

Stepper motors which meet the general definition given above are used, for example, in electronic timepieces to drive the display members thereof which are generally constituted by hands.

US-A 4,371,821 describes a stepping motor, which in this example comprises a stator comprising three pole faces delimiting between them a substantially cylindrical space in which is located the permanent magnet of the rotor whose axis of rotation is substantially coincident with the axis of this cylindrical space.

The permanent magnet of the rotor has a magnetization axis cutting the axis of rotation at an angle of approximately 90 °.

Each pole face occupies an arc of approximately 120 ° in a plan view of the motor, and it is located at a first end of a pole piece.

Each of these first ends of the pole pieces is connected to the first end of the other two pole pieces by zones with high reluctance located on either side of the corresponding pole face.

The second ends of the first and second pole pieces are connected by a first core on which a first coil is wound, and the second ends of the first and third pole pieces are also connected by a second core on which is wound a second coil.

Finally, the stator of the motor comprises means for creating a positioning torque of the rotor which tends to maintain or bring the latter back into one or the other of two rest positions. These rest positions are those in which the magnetization axis of the permanent magnet has a direction called the rest direction which is that of a straight line cutting the axis of rotation of the rotor at an angle of approximately 90 ° and passing through the middle of the first polar face. This straight line is therefore the axis of symmetry of the first pole face, as well as the axis of symmetry of the second and third pole faces with respect to each other.

The magnetic fields produced by the coils when they are traversed by a current therefore have, in the cylindrical space delimited by the polar faces, directions symmetrical to one another with respect to this axis of symmetry.

In another embodiment described in US Pat. No. 4,371,821 mentioned above, the motor stator does not have a pole piece and the two coils, without core, have the shape of substantially flat frames partially surrounding the rotor magnet.

The planes of these coils form an angle, a bisecting plane of which contains the axis of rotation of the rotor.

The directions of the magnetic fields produced by these coils are therefore symmetrical with respect to an axis of symmetry contained in this bisector plane and perpendicular to the axis of rotation of the rotor.

Also in this embodiment, the motor includes means for creating a positioning torque of the rotor which tends to maintain or bring the latter back into one or the other of two angular positions of rest which are again those in which the axis of magnetization of the permanent magnet of the rotor has a direction of rest which is that of the axis of symmetry mentioned above.

The already mentioned US Pat. No. 4,371,821 also describes a motor control method described above.

This process consists in applying to the coils driving pulses formed of two parts. During the first part of each driving pulse, the coils are powered by equal voltages in absolute value whose polarity is such that the magnetic field applied to the rotor magnet and which results from the addition of the magnetic fields produced by these coils has a direction perpendicular to the rest direction defined above and a direction such that the rotor begins to rotate in the desired direction. At the end of the first part of each driving pulse, the polarity of the voltage applied to one of the coils is reversed, so that the resulting magnetic field takes a direction parallel to the direction of rest and a direction opposite to the direction that 'had the magnet axis of the rotor magnet before the start of the driving pulse.

Each of these two parts of the motor pulse lasts a few milliseconds.

This motor has the advantage of providing, all other things being equal, an identical torque in both directions of rotation.

However, for the motor to function properly and at its maximum efficiency, the second part of the driving impulse would have to start when the rotor has turned exactly 90 °.

This is hardly ever the case, since the angle traveled by the rotor during the first part of

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the driving impulse depends on the resistant torque applied to it.

However, when the motor coils are supplied as they are in the first part of the driving pulse, the motor torque has its maximum value when the rotor occupies one of the rest positions and decreases rapidly when this rotor begins to rotate. In addition, when its coils are powered as they are in the second part of the drive pulse, the motor torque is zero when the rotor occupies one of the rest positions and increases relatively slowly depending on the angle of rotation of this rotor.

At the start of the second part of the driving pulse, the torque supplied by the motor therefore has a value which is only a fraction of the maximum torque which it can supply, and this fraction is all the lower as the resisting torque applied to the rotor is large.

As a result, the efficiency of the motor is quite low and, to drive a given mechanical load, it consumes more electrical energy than a conventional stepper motor with only one direction of rotation.

On the other hand, if the resistive torque applied to the rotor is low, this rotor reaches the position where it has rotated 90 ° before the first part of the driving pulse is completed.

The electrical energy supplied to the motor during the end of this first part of the driving pulse is dissipated as a pure loss, which further reduces the efficiency of this motor.

Furthermore, after reaching the above-mentioned position, the rotor oscillates around it until the end of the first part of the driving pulse. There is therefore a non-negligible risk that the second part of the driving pulse will cause the rotor to rotate in the direction opposite to the desired direction instead of making it correctly complete its pitch.

Correct engine operation is therefore not absolutely guaranteed.

In addition, the fact that it is necessary to reverse the direction of the current in one of the coils during each driving pulse makes it difficult to add one of the circuits to the motor control circuit described above. known which are intended to reduce the consumption of a stepping motor by adjusting the duration of the driving pulses supplied to it to the mechanical load which it drives.

US Pat. No. 4,514,676 proposes a method for controlling the motor described above which partly avoids these drawbacks.

According to this method, one of the coils is supplied, alone, to rotate the rotor in one direction, and the other coil is supplied, also alone, to rotate the rotor in the other direction.

For each of the rotor rest positions, the polarity of the voltage applied to the coil corresponding to the desired direction of rotation is chosen so that the magnetic field applied to the rotor magnet does, when this rotor occupies this rest position, an angle of approximately 120 ° with the rest direction of the rotor.

When this motor is controlled according to this process, the torque which it supplies begins by increasing, not passing a maximum when the rotor has rotated by approximately 30 ° and then decreasing.

This variation in the engine torque as a function of the angle of rotation of the rotor is more favorable than in the case where the engine is controlled in the manner described in US Pat. No. 4,371,821 mentioned above. In addition, most of the above-mentioned drawbacks are avoided.

However, since only one coil is supplied, the Joule losses in this coil are higher, all other things being equal, than those which occur when the motor is controlled as described in US-A patent. 4,371,821. The efficiency of the engine is therefore not appreciably improved by this second control method.

US Pat. No. 4,546,278 also describes an engine and its control method which will not be described again here, except to note that this method has roughly the same disadvantages as that which is described in US-A patent. 4,371,821.

An object of the present invention is to provide a stepping motor which provides good efficiency, which is reliable in operation and which is particularly well suited to be combined with an electronic circuit allowing the reduction of consumption by adjusting the driving pulses to the mechanical load involved.

This object is achieved by the claimed motor, which is characterized in that it further comprises means for simultaneously supplying first and second currents to the coils of the motor each time the rotor must turn one step, these means being capable of supplying said currents with a constant direction during the total duration of their supply to the coils and with intensities such that, at the start of said current supply and when the rotor occupies one of its rest positions, said first resulting field forms an angle between 110 ° and 160 ° with a second resulting field produced in said permanent magnet by the second and third magnetic fields of the coils.

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

- fig. 1 is a schematic plan view of an embodiment of the engine according to the invention;

- fig. 2 is a table illustrating a method for controlling the motor of FIG. 1;

- fig. 3 is a diagram of an example of a motor control circuit of FIG. 1, and which implements the engine control method illustrated in FIG. 2; and

- fig. 4 is a partial diagram of another example of the motor control circuit of FIG. 1.

Like one of the motors described in US-A 4,371,821 already mentioned, the motor 1 shown diagrammatically in plan in FIG. 1 by way of nonlimiting example comprises a stator 2 pierced with a substantially cylindrical opening 3.

The cylindrical opening 3 is delimited by three

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pole faces 4a, 5a and 6a which each extend over approximately 120 ° and which are respectively located at a first end of three pole pieces 4, 5 and 6.

The two pole faces 5a and 6a are symmetrical to each other with respect to an axis 7, which is diametrical at the opening 3 and which passes through the middle of the pole face 4a. The latter is therefore itself symmetrical with respect to this axis 7.

The pole pieces 4, 5 and 6 are connected two by two by portions 8, 9 and 10 located between the pole faces 4a, 5a and 6a and the dimensions of which are chosen so that their reluctance is significantly higher than that of the others parts of the stator 2.

The stator 2 further comprises two cores 11 and 12 which connect the second end of the pole piece 4 to the second end of the pole piece 5 and, respectively, to the second end of the pole piece 6.

The two coils of the motor 1, designated respectively by the references 13 and 14, are wound on the cores 11 and 12. The terminals of the coil 13, designated by 13a and 13b, and the terminals of the coil 14, designated by 14a and 14b, are intended to be connected to a control circuit not shown in this fig. 1 and an example of which will be described later.

The motor 1 also comprises a rotor 15, the axis of rotation 15a of which coincides with the axis of the opening 3. The rotor 15 comprises a permanent magnet 16 which is the only one shown in FIG. 1 so as not to load the drawing unnecessarily.

In this example, the magnet 16 has only two magnetic poles designated by N and 2.

The coils 13 and 14 are obviously magnetically coupled with this magnet 16. Each of them is therefore crossed by a part of the magnetic field produced by this magnet 16.

These partial magnetic fields each follow a closed path notably crossing the opening 3 and the magnet 16 itself. These paths have not been shown so as not to unnecessarily load FIG. 1.

The field which results, in this magnet 16, from the vector addition of these two partial magnetic fields has been symbolized in FIG. 1 by an arrow 17, and will be designated by the same reference in the remainder of this description.

This resulting field 17 is perpendicular to the axis of rotation 15a of the rotor 15, and it is directed from the south pole S to the north pole N of the magnet 16, like the magnetization axis of the latter. In addition, when the rotor 15 rotates around the axis 15a, this resulting field 17 also rotates around this axis 15a, in the same direction and at the same speed as the rotor 15.

When the coil 13 is supplied with a current which will be designated by 113 in the rest of this description, it creates a second magnetic field which crosses the opening 3 and the magnet 16 perpendicular to the axis of rotation 15a of the rotor 15 and the result of which in the magnet 16 is symbolized by the arrow 18. To simplify the description which follows, this result will be designated as the magnetic field 18.

The direction of the arrow 18 in fig. 1 indicates the direction of the field 18 when the current 113 flows in the coil 13 from its terminal 13a to its terminal 13b. The direction of this field 18 and the direction of this current 113 will be arbitrarily designated as positive in the remainder of this description.

Similarly, when the coil 14 is supplied by a current which will be designated by 114, it creates a third magnetic field which also crosses the opening 3 and the magnet 16 perpendicular to the axis of rotation 15a and the result of which in this magnet 16 is symbolized by the arrow 19 and will be designated as being the magnetic field 19.

The direction of the arrow 19 in fig. 1 indicates the direction of the field 19 when the current 114 flows in the coil 14 from its terminal 14a to its terminal 14b. The direction of this field 19 and the direction of this current 114 will also be designated, arbitrarily, as positive.

It should be noted that when it is a question in the following of this description of angles formed by the magnetic fields 18 and 19 between them or with the resulting field 17, it will be, in the manner which is usual in geometry, angles that the arrows symbolizing these fields 17,18 or 19 would form if these arrows were moved parallel to themselves until their origins coincided. We see that, in the example of FIG. 1, the fields 18 and 19 form between them, according to this definition, an angle of approximately 120 °.

The motor 1 further comprises notches 21 and 22 formed in the wall of the cylindrical opening 3. These notches 21 and 22 are diametrically opposite, and the diameter 23 on which they are located makes an angle of approximately 45 ° with the axis of symmetry 7.

The presence of these notches 21 and 22 causes the application to the rotor 15 of a positioning torque which tends to maintain it or bring it back into one or the other of two stable equilibrium positions, or rest positions. , which are those where the direction of the resulting field 17 is perpendicular to the diameter 23 and therefore forms with the axis of symmetry 7 an angle of approximately 45 °, designated by the reference A in FIG. 1. This direction of the resulting field 17 will be called the direction of rest. It is shown in fig. 1 from the right in phantom 24.

In fig. 1, the rotor 15 occupies one of these rest positions, which will be arbitrarily called the first rest position of this rotor 15. The second rest position of this rotor 15 will obviously be that in which the direction of the resulting field 17 is opposite to the one he has in fig. 1.

The table in fig. 2 illustrates a motor control method according to the invention.

Each of the lines L1, L2, L3 and L4 of this table corresponds to a driving pulse applied to the motor 1.

The sign + or the sign - registered in the columns designated by 113 and 114 indicates that the current 113, respectively the current 114, is positive or negative during the driving pulse corresponding to the line where it is located. In this example, it will be assumed that these currents 113 and 114 are equal, at least in absolute value.

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The arrows drawn in the columns designated by 18 and 19 indicate the direction and the direction of the field 18, respectively 19, created in the magnet 16 by these currents 113, respectively 114. It will also be admitted that, in this example, the coils 13 and 14 are identical, and that the reluctances of the magnetic circuits crossed by the fields which they create are equal. The intensities of fields 18 and 19 are therefore equal.

The arrows in broken lines drawn in column R indicate the direction and the direction that the resulting field 17 normally has at the start of the driving pulse corresponding to the line where they are located.

In each line L1, L2, L3 and L4, the arrow in solid line also drawn in the column R symbolizes the direction and the direction of a magnetic field R which results from the vector addition of fields 18 and 19 created in response to currents 113 and 114 indicated in the same line.

It should be noted that the arrows drawn in columns 18,19 and R have the same direction and the same direction as if they were drawn in fig. 1.

It should be remembered that, in the embodiment of the motor 1 shown in FIG. 1, the pole face 4a is symmetrical with respect to the axis of symmetry 7 and the pole faces 5a and 6a are symmetrical with each other with respect to this same axis 7.

The intensities of the magnetic fields 18 and 19 being also equal in this example, the resulting field R takes a first direction parallel to the axis of symmetry 7, or even coincident with this axis 7, when the currents 113 and 114 have the same direction, or a second direction, perpendicular to the first and therefore to the axis of symmetry 7, when the currents 113 and 114 have opposite directions.

Line L1 of the table in fig. 2 illustrates the driving impulse which is applied to the motor 1 to rotate its rotor 15 by one step in the direction indicated by the arrow 25 in FIG. 1 from its first rest position. This direction of rotation indicated by arrow 25 will be arbitrarily called positive direction of rotation.

During this driving pulse, the two coils 13 and 14 are supplied simultaneously so that the currents 113 and 114 which pass through them are both positive. The magnetic fields 18 and 19 produced by these coils 13 and 14 in response to these currents therefore have the direction and the direction indicated in this line L1, which are moreover identical to those which are indicated in FIG. 1.

Under the conditions mentioned above, the magnetic field R resulting from the vector addition of the fields 18 and 19 therefore has its first direction, that is to say that which is parallel to the axis of symmetry 7, and a direction going towards the polar face 4a.

It is easy to see that, since the direction of rest 24 forms an angle of 45 ° with the axis of symmetry 7, the resulting field R mentioned above forms, at the start of the driving pulse, an angle of 135 ° with the resulting field 17. This angle is designated by B in the table in fig. 2. Its direction, measured from the resulting field 17 towards the resulting field R, is the same as that of the arrow 25 in FIG. 1 and will also be arbitrarily designated as a positive meaning.

The interaction of the fields R and 17 produces a motor torque which causes the rotation of the rotor 15 in the positive direction, provided of course that the currents 113 and 114 have a sufficient intensity. During this rotation of the rotor 15, this motor torque begins to increase and goes through a maximum when the rotor 15 is in the position where the resulting field 17 is perpendicular to the resulting field R, that is to say when it has rotated approximately 45 °.

This motor torque then decreases and, if the driving pulse is not interrupted, it reaches a zero value when the rotor 15 is in the position where the resulting field 17 has the same direction and the same direction as the resulting field R , that is to say when it has turned about 135 °.

In practice, the driving pulse is interrupted before the rotor reaches this position, and the rotor 15 ends its pitch after this interruption of the driving pulse in response, in particular, to the positioning torque created by the presence of the notches 21 and 22, to its kinetic energy and to that of the various mechanical elements it drives.

When it has finished its pitch, the rotor 15 therefore occupies its second rest position.

Line L2 of the table in fig. 2 illustrates the driving pulse which is applied to the motor 1 to rotate its rotor 15 one step in the positive direction from its second rest position.

During this driving pulse, the two coils 13 and 14 are supplied, always simultaneously, so that the currents 113 and 114 which pass through them are both negative.

It is easy to see that, in this case, the resulting field R also has its first direction, but that its direction is opposite to that which it had during the driving impulse corresponding to line L1 of the table in FIG. 2.

The angle B formed by the resulting fields R and 17 therefore again has, at the start of the driving pulse, a value of 135 ° and its direction, always from the resulting field 17 towards the resulting field R, is also positive.

The rotor 15 is therefore again subjected to a driving torque which causes it to rotate in the positive direction.

As in the previous case, the driving pulse is interrupted before the rotor 15 has rotated 135 °, and this rotor 15 ends its pitch in response, in particular, to the positioning torque, to its kinetic energy as well as to that of the various elements that it entails.

When it has completed this step, the rotor 15 therefore again occupies its first rest position.

Line L3 of the table in fig. 2 illustrates the driving pulse which is applied to the motor 1 to rotate the rotor 15 one step in the negative direction from its first rest position.

During this driving pulse, the two coils are supplied, always simultaneously, so that the current 113 is positive and that the current 114 is negative.

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It is easily seen that, under these conditions, the resulting field R has its second direction, that is to say that which is perpendicular to the axis of symmetry 7, and that its direction goes from the polar face 5a towards the face polar 6a.

At the start of the driving pulse, the resulting field R therefore again forms an angle B of approximately 135 ° with the resulting field 17. But this time, the direction of this angle B, always when it is measured from the resulting field 17 towards the resulting field R, is negative.

The rotor 15 is therefore subjected to a motor torque which causes it to rotate in the negative direction.

As above, the driving pulse is interrupted and the rotor 15 ends its pitch in response, in particular, to the positioning torque, its kinetic energy and that of the various mechanical elements which it drives.

When it has completed this step, the rotor 15 therefore occupies its second rest position.

Line L4 of the table in fig. 2 illustrates the driving pulse which is applied to the motor 1 to rotate the rotor 15 one step in the negative direction from this second rest position.

During this driving pulse, the coils 13 and 14 are supplied, always simultaneously, so that the current 113 is negative and that the current 114 is positive.

Under these conditions, the resulting field R again has its second direction, as in the previous case, but its direction goes from the polar face 6a towards the polar face 5a.

At the start of the driving pulse, the resulting field R therefore again has an angle B of 135 ° with the resulting field 17, and the direction of this angle B is again negative.

The rotor 15 is therefore again subjected to a driving torque which causes it to rotate in the negative direction.

As in the previous cases, the rotor 15 ends its pitch, after the driving pulse has been interrupted, in response, in particular, to the positioning torque, to its kinetic energy and to that of the mechanical elements which it drives.

In summary, it can be seen that in order to rotate the rotor 15, motor pulses are applied to the motor 1 during which the two coils 13 and 14 are always supplied simultaneously with voltages whose polarity does not vary.

In addition, these coils 13 and 14 are supplied in such a way that the magnetic field R resulting from the vector addition of the magnetic fields 18 and 19 produced in the magnet 16 by the currents 113 and 114 flowing in these coils 13 and 14, at the start of each driving pulse, an angle B of approximately 135 ° with the resulting field 17, the direction of this angle B, measured from the resulting field 17 towards the resulting field R, being identical to the direction in which the rotor 15 must rotate .

Since the angle B formed by the resulting field 17 with the resulting field R at the start of each driving pulse has a value of 135 °, the torque supplied by the motor 1 has a value which begins to increase and which passes through a maximum when the rotor 15 has rotated 45 °, that is to say when the direction of the resulting field 17 is perpendicular to the direction of the resulting field R.

As the driving impulse is generally interrupted, in practice, when the rotor 15 has rotated by an angle of approximately 50 ° to 70 °, the torque produced by the motor 1 therefore has a value close to its maximum value throughout the duration of the motor impulse.

In addition, since the direction of the current in the coils 13 and 14 of the motor 1 does not change throughout the duration of the driving pulses, there is no unnecessary consumption and / or risk of reversing the direction of rotation of the rotor. such as those which can occur at the end of the first part of these driving pulses when the motor is controlled in the manner described in US Pat. No. 4,371,821 mentioned above.

As a result, all other things being equal, the efficiency of this engine 1 and its operating safety are higher than those of the engine described in this patent US Pat. No. 4,371,821.

The efficiency of the motor 1 is also higher than that of a motor controlled according to the method described in US Pat. No. 4,514,676 which was also mentioned above, owing to the fact that its two coils are supplied simultaneously.

The value of the angle B mentioned above, that is to say 135 °, is that for which the efficiency of the motor 1 is the highest. However, it is possible to choose values for this angle B between approximately 110 ° and 160 ° without its efficiency decreasing too strongly. In particular, a value of this angle B greater than 135 ° makes it possible to obtain from the motor 1 a higher motor torque, at the cost of a slight increase in its consumption.

Fig. 3 shows by way of nonlimiting example the diagram of a circuit for controlling the motor 1 of FIG. 1 as described above using the table in FIG. 2.

In this diagram, only the coils 13 and 14 of the motor 1, with their terminals 13a and 13b, respectively 14a and 14b, have been shown.

The control circuit of fig. 3 comprises six MOS transistors designated by T1 to T6.

The transistors T1, T3 and T5 are of type p, and their source is connected to the positive pole + of a power source not shown.

The transistors T2, T4 and T6 are of type n, and their source is connected to the negative pole - from the same power source.

It will be assumed that the logic states “0” and “1” of the signals which will be mentioned below correspond respectively to the potential of the negative terminal - and to the potential of the positive terminal + of the above-mentioned power source, which also supplies the various electronic components which will be described.

Consequently, the transistors T1, T3 and T5 are conductive or blocked depending on whether the signal applied to their control electrode has the logic state “0” or “1”, and the opposite is valid for the transistors T2, T4 and T6 .

The drains of the transistors T1 and T2 are connected, together, to the terminal 13a of the coil 13.

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The drains of the transistors T3 and T4 are connected, together, to the terminal 14a of the coil 14 and to one of the terminals of a transmission gate P1, the other terminal of which is connected to the terminal 13b of the coil 13.

The drains of the transistors T5 and T6 are connected, together, to the terminal 14b of the coil 14 and to a terminal of a transmission gate P2, the other terminal of which is connected to the terminal 13b of the coil 13.

It should be noted that the transmission doors P1 and P2 are blocked or conductive depending on whether the signal applied to their control electrode is in the "0" or "1" state.

The control electrodes of the transistors T1 to T6 and of the doors P1 and P2 are connected in the manner shown to the outputs s1 to s7 of a logic circuit L comprising AND gates 31 to 36, OR gates 37 and 38, inverters 39 and 40, and a flip-flop 41 of type T.

It will be assumed that the outputs Q and Q of this flip-flop 41 change state each time the signal applied to the input T changes from state "1" to state "0".

The connections of the various components of circuit L with each other and with outputs s1 to s7 will not be described in detail here, because the design of this circuit L, or of a circuit fulfilling the same functions, is easily deduced from its operation which will be described later.

The circuit of fig. 3 also includes a circuit for generating control signals G, the outputs g1 and g2 of which are connected to the inputs e1 and e2 of the logic circuit L.

This circuit G is arranged so that the signal which it produces at its output g1, which will be called signal g1, passes from the logic state “0” to the logic state “1” each time that the motor 1 must receive a driving pulse, that this signal g1 remains in this state "1" for a duration equal to the time that this driving pulse must have for the rotor 15 of the motor 1 to turn correctly by one step, and for this signal g1 to then return in state "0".

This circuit G is also arranged so that the signal which it produces at its output g2, which will be called signal g2, is permanently in the logic state "0" or in the logic state "1" depending on whether the rotor 15 must turn in the positive direction or in the negative direction.

The circuit G will also not be described in detail here, since its constitution depends on the type of device which is equipped with the motor 1 and its design is within the reach of the skilled person.

It is easy to see that, in the case of the circuit of FIG. 3, the control electrodes of all the transistors T1 to T6 and of the gate P2 are in the logic state "0" and that the control electrode of the gate P1 is in the logic state "1" as long as the signal g1 is in state "0", regardless of the state of signal 92.

In this situation the transistors T1, T3 and T5 as well as the gate P1 are conductive, while the transistors T2, T4 and T6 as well as the gate P2 are blocked. The coils 13 and 14 are therefore short-cir-cuitées and no current flows in these coils.

When a driving pulse must be applied to the motor 1, the signal g1 goes to state "1" and remains there for the entire duration that this driving pulse must have.

If the signal g2 and the output Q of flip-flop 41 are in the state "0" when the signal g1 goes to the state "1", the transistors T3 and T5 are blocked and the transistor T6 becomes conductive, the other transistors and the doors P1 and P2 remaining in the state they were previously.

A current therefore flows from terminal + to terminal -of the power source through transistor T1, coil 13, gate P1, coil 14 and transistor T6. In the coils 13 and 14, this current flows from terminal 13a to terminal 13b, respectively from terminal 14a to terminal 14b.

In the two coils 13 and 14, the current therefore has the direction which has been designated above as positive, and the driving pulse which then receives the motor 1 corresponds to that which has been described using the line L1. from the table in fig. 2.

At the end of this driving pulse, that is to say when the signal g1 returns to the state "0", the transistors T3 and T5 become again conductors and the transistors T6 again blocks. In addition, the Q output of flip-flop 41 changes to state "1".

If the signal g2 is always at state "0" at the start of the next driving pulse, that is to say when the signal g1 returns to state "1", these are the transistors T1 and, at again, T3 which are blocked and the transistor T2 which becomes conductive, the other transistors and the gates P1 and P2 remaining in the state they have when the signal g1 is in the state "0".

Under these conditions, a current therefore flows from terminal + to terminal - of the power source through transistor T5, coil 14, gate P1, coil 13 and transistor T2. In the coils 13 and 14, this current flows from terminal 13b to terminal 13a, respectively from terminal 14b to terminal 14a.

In these two coils, the current therefore has the direction defined as negative, and the driving pulse corresponds to that which has been described using line L2 of the table in FIG. 2.

At the end of this driving pulse, the transistors T1 and T3 become conductive again, and the transistor T2 is blocked again. In addition, the output Q of the flip-flop 41 returns to the state "0", so that, if the signal g2 remains in the state "0", the next driving pulse again corresponds to line L1 of the table of fig. 2.

If, on the other hand, the signal g2 is in the state “1” and the output Q of the flip-flop 41 is in the state “0” at the moment when the signal g1 passes to the state “1”, the transistors T3 and T5, as well as the gate P1, are blocked while the transistor T4 and the gate P2 become conductive.

A current therefore flows from terminal + to terminal -of the power source through transistor T1, coil 13, gate P2, coil 14 and transistor T4. This current therefore has the positive direction in the coil 13 and the negative direction in the coil 14, and the driving pulse corresponds to that which has been described using line L3 of the table in FIG. 2.

At the end of this driving pulse, the transistor T4 and the gate P2 are blocked again and the tran5

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sistor T4 and gate P1 become conductive again. In addition, the Q output of flip-flop 41 changes to state "1".

If the signal g2 is still in state "1" when the signal g1 returns to state "1" at the start of the next driving pulse, these are the transistors T1, again, and T5, as well as, at again, the gate P1 which are blocked, while the transistor T2 and, again, the gate P2 become conductive.

A current therefore flows from terminal + to terminal -of the power source through transistor T3, coil 14, gate P2, coil 13 and transistor T2. This current therefore has the positive direction in the coil 14 and the negative direction in the coil 13, and the driving pulse corresponds to that which has been described using line L4 of the table in FIG. 2.

At the end of this driving pulse, the transistors T1 and T5 as well as the gate P1 become again conductive, while the transistor T2 and the gate P2 are blocked again. In addition, the output Q of the flip-flop 41 returns to the state "0", so that, if the signal g2 remains in the state "1", the next driving pulse again corresponds to line L3 of the table of fig. 2.

In the example which has just been described, the motor 1 is controlled in the so-called “constant voltage” manner, since its coils 13 and 14, in series with one another in this particular case, are subjected to the voltage of the control circuit power source for the duration of each driving pulse.

It is obvious that the motor 1 can just as well be controlled in the so-called “constant current” manner, that is to say so that the current flowing in the coils 13 and 14 is at least approximately constant for the duration of each motor pulse.

A circuit implementing such a method is described, for example, in patent application EP-A 0 057 663, in a case where it is used to control a stepping motor with a single coil and a single direction of rotation . The adaptation of this circuit to the case of the motor 1 with two coils 13 and 14 and with two directions of rotation will not be described here because it is within the reach of those skilled in the art.

It is also obvious that the control circuit of the motor 1, of whatever nature, can be associated with a circuit allowing the duration of the driving pulses to be adjusted to the mechanical load driven by this motor. Numerous documents, which cannot be listed here, describe such adjustment circuits, which are therefore well known and will not be described further here.

When the coils 13 and 14 are controlled by a circuit such as that of FIG. 3, they are always connected in series with each other during the driving pulses.

It is obvious that this connection is not the only possible one and that these coils 13 and 14 can also be connected in parallel during each driving pulse, or even in series when the rotor must turn in one direction and in parallel when this rotor must turn the other way.

Control circuits making these connections have not been shown because their design is within the reach of those skilled in the art.

It should also be noted that in the embodiment of the motor 1 shown in FIG. 1, the fields 18 and 19 form an angle of approximately 120 ° when they are both positive or both negative, while they form an angle of approximately 60 ° when they are one positive and the other negative .

If in addition, as has been admitted for the description of the operation of the motor 1 made with the aid of FIG. 2, the magnetic fields 18 and 19 always have the same intensity, which will be designated by J, we see that the intensity of the R field resulting from their vector addition is not the same depending on whether they are both positive or negative , or that they are one positive and the other negative.

In the first case, which is where the rotor 15 turns in the positive direction, the intensity of the resulting field R is equal to J, while in the second case, which is where the rotor 15 turns in the negative direction, it is equal to ^ • J.

The torque produced by motor 1, which is proportional to the intensity of the resulting field R, is therefore

also / 3 times higher when the rotor 15 turns in the negative direction than when this rotor 15 turns in the positive direction.

If necessary, various measures can be taken to eliminate or at least reduce this variation in the torque supplied by the motor 1 as a function of the direction of rotation of its rotor 15.

Thus, for example, it is possible to modify the control circuit of FIG. 3 as shown in FIG. 4.

The doors 31 and 34, the reverser 39 and the rocker 41 visible in this fig. 4 are identical to the elements of FIG. 3 which bear the same references. In addition, the outputs of the doors 31 to 34 are connected in the same way and to the same elements as in FIG. 3. These have not been shown in fig. 4.

In addition to outputs g1 and g2 which deliver the same signals as the outputs g1 and g2 of circuit G in FIG. 3, the circuit G of FIG. 4 has an output g3 which delivers a signal formed by a series of periodic pulses which will be called pulses g3. For a reason which will be made clear later on in this description, the period of these pulses g3 is short compared to the duration of the motor pulses.

The circuit of fig. 4 further comprises an AND gate 42, the output of which is connected to the inputs of the doors 31 and 34 which are connected, in FIG. 3, at the output g1 of the circuit G. The inputs of this gate 42 are respectively connected to this output gl of the circuit G and to the output of a NAND gate 43.

The inputs of this gate 43 are respectively connected to the output g2 and to the output g3 of the circuit G.

It is easily seen that, when the signal g2 is in the state "0", that is to say when the rotor 15 must turn in the positive direction, the circuit of FIG. 4 works exactly like that of FIG. 3.

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On the other hand, when the signal g2 is in the state "1", that is to say when the rotor 15 must turn in the negative direction, the coils 13 and 14 are periodically disconnected from the power source and reset in short-circuit, and this each time the signal g3 is in the state "1". The current flowing in these coils 13 and 14 is not interrupted when this signal g3 is in this state "1", since these coils 13 and 14 have a certain inductivity and they are short-circuited. But, obviously, the value of this current is, at each instant, lower than that which it would have if the coils 13 and 14 remained permanently connected to the power source.

It is therefore sufficient to choose the duty cycle of the pulses g3 so that the value of this current decreases by a factor. The torque produced by the motor 1 is then identical whatever the direction of rotation of the rotor 15.

In the motor 1 shown in FIG. 1, the magnet 16 of the rotor 15 has only two magnetic poles, and the positioning means of this rotor 15, constituted by the notches 22 and 23, are arranged so that the rest direction of the resulting field 17 makes a angle A of 45 ° with the axis of symmetry 7.

This value of the angle A is particularly advantageous, since it is that for which the efficiency of the motor 1 is the highest when it is controlled in the particularly simple manner described above, that is to say when the currents 113 and 114 are equal.

However, it is possible to arrange the means for positioning the rotor 15 so that the value of this angle A is between approximately 20 ° and approximately 70 ° without modifying this manner of controlling the motor 1, and without, however, the efficiency of the latter decreases too strongly.

We also see that, depending on the value of the angle A, it is possible that, with the sense conventions defined above, the fields 18 and 19, and therefore the currents 113 and 114, must have different meanings l ' to each other during the driving pulses intended to rotate the rotor 15 in the positive direction, and that these currents 113 and 114 must have the same direction during the driving pulses intended to rotate the rotor 15 in the negative direction.

To describe the process for controlling the motor 1 in such a case, it is therefore more advantageous to define respectively as first and second direction of the current 113 or of the current 114 the direction that this current 113 or 114 has during the driving pulses intended to make turn the rotor 15 in its first direction of rotation from its first and, respectively, from its second rest position.

With these definitions, and whatever the angle A, it can be said that, for the rotor 15 to rotate in its first direction, the currents 113 and 114 must both have their first and second directions alternately and that, in order for ie rotor 15 rotates in its second direction, current 113 must have its first and second directions alternately and current 114 must have its second direction when current 113 has its first direction and vice versa.

Knowing the angle A, it is easy to determine the intensities and the directions that the currents 113 and 114

must have during each of the driving impulses so that the angle B has the desired value. This determination can be made using simple three-dimensional calculations which will not be described here.

Furthermore, it is easily seen that, whatever the number P of magnetic poles of the rotor magnet, which then has P distinct rest positions, there is always, in the permanent magnet, a magnetic field similar to the resulting field. 17 described in the case of the motor 1 of FIG. 1, that is to say a field resulting from the vector addition of the two partial fields produced by the magnet and each passing through one of the coils.

Always regardless of the number P of magnetic poles of the rotor magnet, this resulting field has a direction and a direction which depend on the angular position of the rotor, and it rotates 180 ° in the same direction as the rotor each time that the latter rotates by an angle equal to that which separates, in the permanent magnet, two adjacent magnetic poles, i.e. 3607P, or, which is equivalent, by an angle equal to that which separates two successive rest positions of the rotor.

As in the case of an engine whose rotor comprises a bipolar magnet, which is only a particular case of a magnet in which the number P mentioned above is equal to two, it is the interaction of this resulting field with that which is produced by ies coils in response to the currents which cross them which produces the engine torque causing the rotation of the rotor.

It should also be noted that this motor according to the invention can be provided with a rotor comprising a permanent magnet having more than two magnetic poles, this motor being able to be advantageously controlled, in particular when the means for positioning its rotor are arranged so that the resulting field similar to field 17 defined above makes, in each of the rest positions of this rotor, an angle preferably equal to approximately 45 ° with the axis of symmetry of the directions of the magnetic fields produced, in the magnet permanent, by the motor coils when these are traversed by a current. This angle, which is similar to the angle A in fig. 1, may moreover be between 20 ° and 70 ° without the operation of this engine being significantly affected.

Such an engine has not been shown, because it can be identical to the engine 1 of FIG. 1 in which the bipolar magnet 16 has simply been replaced by a magnet having more than two magnetic poles.

Claims (4)

Claims 1. Stepper motor with two directions of rotation comprising: - a rotor comprising a permanent magnet producing a first magnetic field; - A first coil crossed by a first part of said first magnetic field and intended to produce a second magnetic field in response to a first current; a second coil crossed by a second part of said first field and intended to produce a third magnetic field in response to a two- 5 10 15 20 25 30 35 40 45 50 55 60 65 17 CH 680 253G A3 x current, said first and second parts of said first magnetic field forming in the permanent magnet a first resulting field; - first means for applying said second magnetic field to said permanent magnet in a first direction; - second means for applying said third magnetic field to said permanent magnet in a second direction symmetrical to the first direction with respect to an axis of symmetry; and - positioning means intended to maintain or bring said rotor into one or the other of a plurality of rest positions, characterized in that it also comprises means for simultaneously supplying said first and second currents to coils each time the rotor must turn one step, these means being capable of supplying said current with a constant direction during the total duration of their supply to the coils and with intensities such that, at the start of said current supply and when the rotor occupies one of its rest positions, said first resulting field forms an angle (B) of between 110 ° and 160 ° with a second resulting field produced in said permanent magnet by said second and third magnetic fields. 2. Stepping motor according to ia claim 1, characterized in that the angle (B) has a value substantially equal to 135 °. 3. Stepping motor according to claim 1 or 2, characterized in that said first and second currents have an equal intensity, the positioning means being arranged further so that, in each of said rest positions, said first magnetic field resulting made with the axis of symmetry an angle (A) between 20 ° and 70 °. 4. Stepping motor according to claim 3, characterized in that said angle (A) has a value substantially equal to 45 °. 5 10 15 20 25 30 35 40 45 50 55 60 65 11