Control circuit of a stepping motor capable of detecting an external magnetic field

Abstract

To provide an electronic control circuit of a stepping-type motor detecting presence of an external magnetic field.SOLUTION: In a control circuit 20 of a stepping-type motor 2, especially a clock motor, having a bipolar permanent magnet 6, a stator 4, and a coil 18 mounted to a magnetic circuit of the stator 4, a control circuit 20 includes means for determining a position of a rotor when it is still, an electric pulse generator 22, and a circuit 24 for detecting an external magnetic field that is formed of a circuit 26 for measuring current in a coil after an electric pulse is triggered, a circuit 28 for comparing the measured current with a reference current, a circuit 32 for measuring time that can measure rising time until current flowing in a coil reaches the reference current after an electric pulse is triggered, and a circuit 36 for processing rising time that is constituted so as to be capable of determining whether the measured rising time shows presence of a given external magnetic field passing through two narrow parts following a direction orthogonal to an alignment direction 14 of the two narrow parts.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control circuit for a stepper motor that is arranged to detect magnetic fields external to the motor and present in the environment of this motor.

[0002] In particular, stepping motors are timepiece motors, especially rabbet type motors, which are integrated into electromechanical movements to form electronic watches with analogue displays. [Background technology]

[0003] U.S. Patent No. 11,176,632 describes an electromechanical timepiece including a rabbet-type stepping motor having a rotor with a bipolar permanent magnet and a coil mounted on a magnetic circuit formed by a stator that has a circular opening for the magnet and defines two diametrically opposed isthmis around the periphery of the opening that separate the two poles of the stator and direct the magnetic flux generated by the coil across the opening.

[0004] The motor is associated with a control circuit that manages the power supply of the coils, which supplies a series of electrical pulses to said coils in order to drive the rotor in rotation. Each series has electrical pulses with the same polarity and is intended to execute one motor step, each series having alternating opposite first and second polarities. Depending on the torque required to execute each motor step, other constraints applied to the rotor, or disturbances being applied to the motor, the electrical pulses have a variable duration within and / or between the series. This technique is called Pulse Width Modulation (PWM) and is well known. It can be observed that the number of electrical pulses in a series to execute a motor step varies according to the physical events mentioned above.

[0005] US Patent No. 11,176,632 teaches that an external magnetic field oriented according to the direction defined by the two poles of the stator affects two parameters of a series of electric pulses that vary according to the polarity of these series. More specifically, it can be observed that the number of electric pulses in each series as well as the maximum duration of these electric pulses vary according to the polarity in the presence of said magnetic field (it is understood that this magnetic field has an intensity capable of generating disturbances in the operation of the motor, at least in certain modes, in particular in the high speed drive mode of the rotor). It is therefore suggested to detect the presence of an external magnetic field that causes disturbances based on a comparison of either the maximum duration or the number of these pulses between series with opposite polarity, i.e. positive and negative polarity.

[0006] This technique, as illustrated in the above mentioned US publication, is relatively complex to implement and is only possible in the case of control of motors using pulse width modulation techniques. Summary of the Invention

[0007] The object of the present invention is to provide an electronic control circuit for a stepping motor, comprising a circuit for detecting an external magnetic field adapted to control a motor which generates continuous-type motor drive pulses, i.e. at a constant voltage for the duration of each drive pulse of the rotor of said motor (hence without "PWM").

[0008] Another object of the present invention is to provide an effective and relatively uncomplicated method of sensing an external magnetic field via an evolutionary control circuit for a stepper motor by utilizing physical phenomena different from those taught in the prior art and demonstrated through the development leading to the present invention.

[0009] The present invention relates to an electronic control circuit for a stepper motor, the motor comprising a rotor with a bipolar permanent magnet with a magnetization axis perpendicular to the rotor's axis of rotation, and a stator defining an opening forming a magnetic circuit and a housing for the permanent magnet. The stator also defines two isthmuses diametrically opposed around the opening in a first direction perpendicular to the axis of rotation, and two rest positions of the rotor in which the permanent magnets are oriented in a second direction angularly offset in both directions from the first direction, respectively. The permanent magnets generate a first magnetic flux passing through the two isthmuses in both directions, respectively, in the two rest positions, the first rest position corresponding to a positive directionality of the first magnetic flux and the second rest position corresponding to a negative directionality of the first magnetic flux, by definition. The motor further comprises a coil mounted in the magnetic circuit such that when a positive or negative electric pulse is supplied, the coil is capable of generating a second magnetic flux passing through the two isthmuses in the positive and negative directionality, respectively. The electrical control circuit comprises means for determining a stationary rotor position among a first and a second stationary position, and an electrical pulse generator associated with the power supply and configured to selectively supply positive and negative electrical pulses to the coil.Furthermore, the electronic control circuit comprises a circuit for detecting an external magnetic field generated by the circuit for measuring the current, a circuit for comparing the measured current with a reference current, a time measurement circuit configured to measure the rise time from when one of the electrical pulses is triggered to the next moment when the current through the coil reaches the reference current, and a circuit for processing the rise time configured to be able to determine whether the measured rise time indicates the presence of a given external magnetic field passing through the two isthmuses.

[0010] According to two main variants, the circuitry processing the rise time is configured to be able to determine, at least approximately within a range of useful values, the strength of the external magnetic field or its magnetic flux passing through the two isthmuses as appropriate, or whether the strength of the external magnetic field or the strength of the magnetic flux passing through the two isthmuses is greater than a reference value.

[0011] According to a particular variant, the circuitry for processing the rise time is configured to be able to determine, at least within a range of valid values, whether the strength of the external magnetic field or its magnetic flux passing appropriately through the two isthmuses is within a particular range of values ​​of a number of consecutive predetermined values.

[0012] According to an advantageous embodiment, the circuitry processing the rise time is configured so as to be able to determine the directionality of the external magnetic field passing appropriately through the two isthmuses.

[0013] According to a preferred embodiment, the control circuit is configured to detect the presence of a given external magnetic field by generating an electrical pulse in antiphase with the rotor's rest position, i.e. a negative electrical pulse when the rotor is in a positive rest position and a positive electrical pulse when the rotor is in a negative rest position, so that detection of an external magnetic field does not cause the rotor to move forward one step.

[0014] A feature of the present invention allows the detection of the presence of an external magnetic field based on the rise time of the current in the coils of the motor to a predefined reference time after a potentially relatively short electrical pulse (detection pulse) is triggered, the conditions of which relate to the rest position of the rotor when the detection pulse is triggered and the direction and orientation of the external magnetic field relative to the stator, as will become more clear in the detailed description of the invention.

[0015] The invention relates to an electromechanical movement including a stepper motor arranged according to the invention and a control circuit for said motor, said motor comprising a rotor with a bipolar permanent magnet (hereinafter also called "permanent magnet" or "magnet") with a magnetization axis perpendicular to the axis of rotation of said rotor, and a stator defining an opening forming a magnetic circuit and a housing for the permanent magnet. The stator defines two isthmuses diametrically opposed around the opening in a first direction perpendicular to the axis of rotation, and two rest positions of the rotor in which the permanent magnets are oriented in a second direction angularly offset in both directions from the first direction, respectively. In both rest positions, the permanent magnets generate a first magnetic flux passing through the two isthmuses respectively in both directions, the first rest position corresponding by definition to a positive directionality of the first magnetic flux and the second rest position corresponding to a negative directionality of the first magnetic flux. The motor further comprises a coil mounted in the magnetic circuit so as to generate a second magnetic flux passing through the two isthmuses in a positive and negative sense, respectively, when supplied with a positive or negative electric pulse.The invention also relates to a wristwatch incorporating an electromechanical movement according to the invention.

[0016] Furthermore, the invention also relates to a method for detecting an external magnetic field in which a stepping motor, in particular a timepiece motor, controlled by an electronic control circuit according to the invention is located. [Brief description of the drawings]

[0017] The invention is explained in more detail below with reference to the accompanying drawings, given as non-limiting examples, in which: [Figure 1] 1 is a schematic diagram of a general embodiment of a stepping and single-phase type clock motor and a circuit for controlling this motor according to the invention; [Diagram 2] FIG. 2 is a schematic diagram of the clock motor of FIG. 1, showing the magnetic flux of the rotor magnets in the two isthmuses of the stator; [Diagram 3] 1 is a graph showing the curves of the rotor magnet flux in the two isthmuses of the stator as a function of the angular position of the magnet. [Figure 4]FIG. 2 is a schematic diagram of the timepiece motor of FIG. 1, illustrating diagrammatically the magnetic flux generated by the coil during a positive electrical pulse. [Diagram 5] 1 is a graph showing two curves of magnetic flux generated by currents in the negative and positive coils, respectively, in the two isthmuses of the stator and the core of the coil. [Figure 6] FIG. 2 is a schematic diagram of the timepiece motor of FIG. 1 showing the circulation of an external magnetic field within the stator, this external magnetic field being located in the plane of the stator and propagating in a positive direction according to a direction approximately perpendicular to the alignment direction of the two isthmuses. [Figure 7] 7 is a schematic view of the timepiece motor of FIG. 1 similar to FIG. 6, but for the negative directionality of the external magnetic field according to the general direction mentioned above. [Figure 8] 1 is a graph showing the curves of the external magnetic flux passing through the two isthmuses of the stator as a function of the strength of the external magnetic field in the absence of other magnetic fluxes. [Figure 9] 9A to 9D show four curves of the evolution of the current in the coil after an electric pulse has been triggered, as a function of various conditions regarding the rest position of the magnet and the polarity of the electric pulse, in the absence of an external magnetic field. [Figure 10] 10A to 10D respectively show four curves of the evolution of the current in the coil after an electric pulse has been triggered as a function of various conditions regarding the rest position of the magnet and the polarity of the electric pulse, in the presence of an external magnetic field of positive directionality, as shown in FIG. [Figure 11] Figures 11A and 11B are two graphs showing the curves of the evolution of the current in the coil after an electric pulse has been triggered, for the magnet in a positive rest position and an in-phase electric pulse (positive polarity), respectively, for two negative and positive directions of the external magnetic field according to Figures 6 and 7, depending on the various strengths of this external magnetic field. [Figure 12] Figures 12A and 12B are two graphs showing the curves of the evolution of the current in the coil after an electric pulse has been triggered, for the magnet in a positive rest position and for an antiphase electric pulse (negative polarity), respectively, for two negative and positive directions of the external magnetic field according to Figures 6 and 7, depending on the various strengths of this external magnetic field. [Figure 13] 1 is a table showing the evolution of the current rise over time in the coil after an electric pulse is triggered, for zero or a weak external magnetic field and for a relatively strong external magnetic field, in various possible magnetic configurations in the two isthmuses of the stator. [Figure 14] 1 is a table showing the duration of the rise time of the current to a reference intensity upon triggering of an electrical pulse as a function of the rest position of the magnet, the polarity of the electrical pulse, and various intensities of the bidirectional external magnetic flux. [Figure 15] FIG. 1 discloses a method for detecting a given external magnetic field for an in-phase electrical pulse. [Figure 16] FIG. 10 discloses a method for detecting a given external magnetic field for an anti-phase electrical pulse. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An electronic control circuit 20 for a stepping motor 2, in particular a watch motor, is described with reference to the attached drawings. The physical phenomenon used by a detection circuit 24 integrated in the electronic control circuit and arranged to detect an external magnetic field around the motor, and the method of detecting an external magnetic field realised by this detection circuit are described in detail.

[0019] The motor 2 comprises a rotor 3 with a bipolar permanent magnet 6 having a magnetization axis perpendicular to the axis of rotation 7 of the rotor, and a stator 4 defining an opening 8 forming a magnetic circuit and a housing for the permanent magnet 6. The stator further defines two diametrically opposed isthmuses 12a and 12b in a first direction 14 perpendicular to the axis of rotation 7, and two stable rest positions of the permanent magnet, i.e. of the rotor, in which the magnetization axis is oriented in a second direction 16 angularly offset in both directions from the first direction 14, respectively. The two rest positions are conventionally determined by two diametrically opposed notches 10a and 10b provided at the ends of the opening 8. The permanent magnet 6, in each of its two rest positions, is axially oriented in both directions by a first magnetic flux F passing through the two isthmuses respectively. AThe isthmuses 12a and 12b are arranged such that the magnetic flux passing through any isthmus passes through it primarily according to a third direction 40 (shown in FIG. 2) that is perpendicular to the first direction 14. The first rest position, also called the positive rest position, is +F A The first magnetic flux F at the two isthmuses shown as (see Fig. 2) A The second rest position, also called the negative rest position, corresponds to the positive direction of −F A The first magnetic flux F at the two isthmuses shown as A 3 shows the magnetic flux F as a function of the angular position of the permanent magnet 6 (counterclockwise direction). A 4 is a graph showing a curve 42 of the permanent magnet and thus of the rotor. The positive rest position PR1 of the permanent magnet and therefore of the rotor is 0° and the negative rest position PR2 is 180°. It can be observed that the magnetic flux of the permanent magnet saturates to some extent the two isthmuses of the stator in both rest positions. In the absence of magnetic saturation, the curve is substantially sinusoidal.

[0020] Motor 2 receives a positive electrical pulse +I B (t) or negative electric pulse-I B When (t) is supplied, the positive direction +F B (FIG. 4) and the negative orientation -F B In each of the two isthmuses, a second magnetic flux F passes through the two isthmuses mainly in a third direction 40. B 5 shows the current I in the coil in the absence of the rotor magnet flux and other magnetic flux. B As a function of the strength of (t), the magnetic flux F generated by the coil 18 in the two isthmuses 12a and 12b is B 3 and 5 show a curve 46 of the current (t) and a corresponding curve 48 of the magnetic flux propagating in the core of the coil. It can be observed that the magnetic flux in the core increases practically linearly with increasing current intensity, while the magnetic flux in the isthmus rapidly saturates, already at about 0.05 mA. As can be seen from Figs. 3 and 5, the magnetic flux generated by the coil in the stator rapidly becomes higher than the magnetic flux generated by the permanent magnet. As a result, the magnetic flux F of the coil 16B gives the directionality of the magnetic flux in the two isthmuses after a certain delay has elapsed since the electric pulse was triggered, which is the direction of the magnetic flux in the two isthmuses of the magnet F A Even though the magnetic flux in the coil has a direction opposite to that of the coil in the two isthmuses, it quickly reaches saturation (a value of about 100 nWb in the given example).

[0021] The electronic control circuit 20 comprises means for determining the position of the rotor at rest among a first and a second rest position, associated with a power supply and for transmitting a positive electric pulse +I, in particular with a voltage between about 1 V and 3 V. B (t) and negative electric pulse-I B and an electric pulse generator 22 configured to selectively supply an external magnetic field H(t) to the coils. The generator 22 generates an external magnetic field H(t) together with electric pulses (drive pulses) for rotating the rotor, as described in more detail below. Ext In particular, the managing circuit 38 manages the generation of the electric pulses supplied to the coil. It should be noted that the electric drive pulses may also jointly form the electric detection pulses. If not associated with other qualifiers, the term "electric pulse" is understood in this specification to mean an electric detection pulse (detection pulse). Means for determining the positive or negative rest position of the rotor are known to the person skilled in the art and are typically provided in the control circuit of the timepiece stepping motor. The electronic control circuit 20 is connected to the managing circuit 38 and is adapted to detect the external magnetic field H Ext The coil further includes a circuit 24 for detecting the intensity I B A circuit 26 for measuring (t) and the intensity of the measured current I B (t) as reference current I Ref and a circuit 28 for comparing the intensity I of the current flowing through the coil from the trigger of each electrical detection pulse. B (t) is the reference current I Ref The rise time T M and a time measurement circuit 32 that allows measurement of the measured rise time T M is a given external magnetic field H passing through the isthmus 12a and 12b according to a third direction 40 during the considered electrical detection pulse.Ext and a circuit 36 ​​for processing the rise time configured to be able to determine whether a rise time indicates the presence of a stator current source 8 (which results from the shape of the isthmus that defines two narrowings for the magnetic flux in the stator, these being oriented tangentially to the aperture 8, which is substantially circular).

[0022] In particular, the comparison circuit 28 compares the intensity I of the coil current provided by the measurement circuit 26 after the electrical detection pulse is triggered. B (t) and the reference current I Ref It receives as input and has intensity I B (t) is the reference value I Ref Comparison signal S indicating whether C The detection circuit 24 has a comparator 29 which outputs the measured current intensity I B (t) can be monitored in near real time, while the rise time T M A time base 34 is provided that provides a relatively high speed clock signal, for example a clock signal of about 500 kHz or higher, so as to accurately determine

[0023] 6 and 7 show the external magnetic field H Ext , the main component of which propagates approximately in the plane of the stator according to a direction 40, i.e. a direction perpendicular to the alignment direction 14 of the two isthmuses 12a and 12b, and which, in a positive direction, produces a magnetic flux +F H In the negative direction, the magnetic flux -F H In addition, the external magnetic field H Ext What is important in the detection method is the magnetic flux passing through the two isthmuses, that is, the magnetic flux F passing through the two isthmuses between the two poles 4A and 4B of the stator 4. H This is called the "external magnetic flux". Figure 8 shows the external magnetic field H Ext As a function of the strength of the magnetic flux F in the two isthmuses of the stator, H1 shows a curve 50 of the external magnetic field H 2 . It can be observed that when the strength of the external magnetic field is increased, the external magnetic flux saturates the two isthmuses. Ext The strength of the external magnetic field ranges from 1,000 A / m, i.e., up to about 2,000 A / m. However, the detection method according to the present invention is not limited to external magnetic fields of less than 2,000 A / m.

[0024] 9A to 9D show four curves of the evolution over time of the current in the coil after the electrical detection pulse has been triggered, for the positive and negative rest positions of the rotor and, for each of these two rest positions, for a positive electrical pulse and a negative electrical pulse, in the absence of an external magnetic field in the isthmus. In connection with the development of the electronic control circuit of the stepping motor that led to the invention, the inventors made the following observations: The magnetic flux F of the permanent magnet in the two isthmuses A The magnetic flux F of the coil at these two isthmuses is B 9A) or negative rest position and negative current (FIG. 9B). B (t) increases relatively quickly after the electrical pulse is triggered (rapid increase in current and fast reference current I Ref Rise time to T M On the other hand, the magnetic flux F of the permanent magnet at the two isthmuses is A The magnetic flux F of the coil at these two isthmuses is B When the current has an opposite direction to that of the reference current I, i.e., either a positive resting position and a negative current (FIG. 9C), or a negative resting position and a positive current (FIG. 9D), the current increases relatively slowly after the electrical pulse is triggered (a gradual increase in current and a slow reference current I Ref Rise time to T M (This article discusses the following.)

[0025] The current I in the coil after the detection pulse is triggered B The four curves of the evolution of (t) over time are shown for the four configurations in Figures 9A-9D and for the two isthmuses with relatively strong positive external magnetic flux, i.e. +F HA relatively positive external magnetic field H Ext , i.e. +H Ext 10A to 10D for = +1,600 A / m. When the current and the external magnetic field have the same sign, i.e., the magnetic flux F B and external magnetic flux F H have the same directionality (here positive), the current I B It can be observed that (t) increases relatively rapidly after the electric pulse is triggered, regardless of the fact that the permanent magnet 6 is in a positive or negative rest position. On the contrary, when the current and the external magnetic field have opposite signs, i.e., the magnetic flux F of the coil B (here negative) and the external magnetic flux F H (here positive) has the opposite direction, the current I B (t) increases relatively slowly after the electrical pulse is triggered, regardless of the fact that the permanent magnet is in a positive or negative rest position.

[0026] Therefore, after an electric pulse supplied to this coil is triggered, the magnetic flux F 1 passes through the two isthmuses of the stator 4 and is generated by the permanent magnets 6 of the rotor 3. A A relatively strong external magnetic flux F with a direction opposite to that H Therefore, when the external magnetic field is positive and the permanent magnet / rotor is in a negative rest position (FIGS. 10B and 10D), or when the external magnetic field is negative and the permanent magnet / rotor is in a positive rest position, the current I flows through the coil. B It can be seen that there is a change in the evolution of (t). More specifically, when the rotor permanent magnet is in phase with the electrical detection pulse (magnetic flux F generated by the coil B The magnetic flux F of a magnet with the same direction / sign as A ), the current intensity I B (t) is the external magnetic field H Ext In the absence of H In the presence of an external magnetic field that generates a current I BSince the rise of (t) changes from "fast" to "slow", the relatively strong external magnetic field H Ext In the presence of a current I B (t) Rise time T M will be longer.

[0027] Conversely, when the rotor permanent magnet is in antiphase with the electrical detection pulse (magnetic flux F generated by the coil B The magnetic flux F of a magnet with opposite direction / sign is A ), the current intensity I B (t) is the external magnetic field H Ext In the absence of , it increases slowly, but there is a relatively strong external magnetic flux F of opposite sign / direction to the rotor magnet. H In this way, the relatively strong external magnetic field H Ext In the presence of a current I B Since the rise of (t) changes from "slow" to "fast", the current I B (t) Rise time T M The method of detecting an external magnetic field according to the present invention is based on this physical phenomenon and can be implemented by knowing the rest position of the rotor when the electrical detection pulse is triggered (information necessary to provide the electrical drive pulse) and with known polarity to determine the rise time T M (i.e., this information is given at the time of occurrence of an electrical pulse, whether it is a positive or negative electrical pulse).

[0028] 11A and 11B show the current I in the coil when the permanent magnet is in a positive rest position for an in-phase electrical pulse, hence a positive pulse, and there is a negative and positive external magnetic field, respectively, for various strengths of the external magnetic field. B 11A shows the physical phenomenon described for a negative external magnetic field. FIG. 11B shows the physical phenomenon when the external magnetic field has the same direction / sign as the rest position of the permanent magnet, i.e., the external magnetic flux F H and the magnetic flux of the magnet F A12A and 12B show that when the permanent magnet is in a rest position with electrical pulses of opposite phase, and thus positive for negative pulses, and with negative and positive external magnetic fields, respectively, for various strengths of the external magnetic field, the current I in the coil changes very little over time and remains fast. B 12A shows the physical phenomenon described above. FIG. 12B shows the current I in the coil when the external magnetic field has the same sign as the rest position of the permanent magnet. B We again show that (t) changes very little over time and remains slow.

[0029] The table of FIG. 13 shows the current I in coil 18 when the electrical detection pulse is triggered. B (t) rise and reference current I Ref The rise time T M The table of FIG. 14 reproduces in another form and numerically the findings of FIG. 13 with different values ​​of the external magnetic field. The rise time T as a function of the initial conditions regarding the rest position of the permanent magnet and the polarity of the electrical detection pulse in the presence or absence of a relatively strong external magnetic field. M A physical explanation can be given for the case of a varying or non-varying external magnetic field, and more generally for the case of a gradually increasing strength of this external magnetic field. S Current in the coil as a function of I B The equation for (t) contains a second term related to the voltage induced by the variation in current. To a first approximation, we have the following equation for the current: V S =RI B (t)+LdI B (t) / dt Here, V S is the constant voltage applied to the coil, R is the electrical resistance of the coil, and L is the inductance of the coil.

[0030] The inductance L of the coil is related to the permeability (the inverse of the magnetic reluctance) of the magnetic circuit defined by the stator and comprising the core to which the coil is attached. However, the permeability of the magnetic circuit formed by the stator of the coil varies with the degree of magnetic saturation of the two isthmuses 12a and 12b. Thus, the inductance L of the coil also varies with the degree of magnetic saturation of the two isthmuses. More precisely, when the two isthmuses are not saturated or are barely saturated, the inductance L is relatively high, and when the two isthmuses are fully saturated or fully saturated, this inductance L is relatively low. This results in the equation for the aforementioned voltage being: For a given supply voltage V S On the other hand, when the inductance L is high, the change in current over time dI B (t) / dt is slow, and when the inductance L is relatively low, the change in current over time dI B (t) / dt is relatively fast. Therefore, if the inductance L is high, the reference current I Ref Current I B (t) Rise time T M Conversely, when the inductance L is low, the reference current I Ref Current I B (t) Rise time T M becomes relatively short.

[0031] The above physical phenomenon occurs due to the external magnetic field H Ext In order to understand the results given in the tables of Figs. 13 and 14, first consider the magnet flux F of the isthmus 12a and 12b. A It is pointed out that the magnetic field H detected must magnetically saturate these two isthmuses to a significant degree in both of its rest positions. This is generally the case for clock motors with bipolar permanent magnets, in particular of the rabbet type (corresponding to the one shown and described above). Then, the external magnetic field H detected Ext is the magnetic flux of the permanent magnet F A At least as large as F A An external magnetic flux F with a strength higher than Hat the two isthmuses, so that the superposition of these two fluxes, if they have opposite senses, will significantly reduce the reluctance of the magnetic circuit, or the flux F A , with the resulting magnetic flux directionality at the two isthmuses reversed with respect to . Finally, the coil is at least 100% of the magnetic flux F of the magnet after a time interval shorter than the duration of the electrical detection pulse. A Preferably as large as F A The magnetic flux F in the two isthmuses is higher than B In practice, in a clock motor with bipolar permanent magnets, the magnetic flux F is supplied to the rotor, as shown by the curve 46 in FIG. B Only (t) strongly saturates the two isthmuses after a given initial time interval.

[0032] The results in Tables 13 and 14 can be explained as follows. H If there is no current I B When L(t) is in phase with the rest position of the permanent magnet (same directionality, and therefore sign, of the magnetic flux in the two isthmuses), this current only increases the magnetic saturation of the two isthmuses, which were initially saturated at a relatively high level. Thus, the inductance L(t) remains low throughout the electrical detection pulse, and rise time T M is short. Conversely, the current I B If (t) is in antiphase with the rest position of the permanent magnet (opposite directionality of the magnetic flux in the two isthmuses, and therefore opposite sign), the magnetic flux F B (t) decreases at least momentarily during the initial time interval of the electrical detection pulse, leading to magnetic saturation at the two isthmuses (the saturation generally becomes high again after the initial time interval, and the magnetic flux F B (Note that the current rise time T(t) is longer when the direction of the magnetic flux at the two isthmuses is reversed.) Thus, during the initial time interval, the inductance L(t) of the coil increases and becomes higher for a short period of time, thereby shortening the current rise time T MTherefore, to understand the obtained results, it is necessary to take into account not only the end situation at the end of the electric pulse, but also the evolution of the inductance over time.

[0033] External magnetic field H Ext If there exists an external magnetic flux F H is the magnetic flux of the permanent magnet F A When the external magnetic field has the same directionality / sign as H, the situation is in fact substantially similar to that described in the previous paragraph, since it slightly increases the initial magnetic saturation of the magnet, which is already relatively high. Therefore, the external magnetic field H Ext does not significantly change the change in inductance L(t) during the electrical detection pulse, but only introduces a small delay (time offset) in the temporary increase in inductance L(t) when the permanent magnet and electrical detection pulses are in antiphase, which is related to the coil current I B (t) is reflected in the small initial increase in the external magnetic flux F H is the magnetic flux of the permanent magnet F A When the external magnetic flux F has a direction opposite to that of the H changes the initial conditions for magnetic saturation in the two isthmuses and / or the initial directionality of the initial total magnetic flux in these two isthmuses, thereby changing the external magnetic field HE xt When the strength of the external magnetic field becomes sufficiently high, the evolution of the inductance L(t) over time for the two polarities of the electrical detection pulse changes significantly, at least within the range of values ​​that are valid for the strength of the external magnetic field.

[0034] In particular, when the electrical pulse is in phase with the rotor's rest position, the magnetic flux F A The magnetic flux F at two isthmuses with opposite directions H The external magnetic field that generates the magnetic flux F B The rise time T(t) at least momentarily reduces the magnetic saturation, thereby increasing the inductance L(t). M increases, which is at least within the range of values ​​given for this strength between zero and the determined maximum value, HIn the example of Figure 14, the maximum value considered is equal to about 2,000 A / m. When the electric pulse is in antiphase with the rest position of the rotor, the magnetic flux F of the permanent magnet A At the two isthmuses in the opposite direction to the external magnetic flux F H The external magnetic field that generates the magnetic flux F B (t) and further reduce the external magnetic flux F H When has a sufficiently high strength, the external magnetic flux F H Since the inductance L(t) is reduced at least momentarily during the electrical detection pulse, counteracting the reduction in magnetic saturation of the isthmus that would occur in the absence of M decreases, which means that the external magnetic flux F H It gradually decreases as the intensity of increases.

[0035] An important observation can be made from the above disclosure: when the rotor / permanent magnet is in a negative rest position, within the effective range of its strength, a positive external magnetic flux F H (F H ) only generates an external magnetic field with a rise time T M is easily detected based on the negative external magnetic flux F when the rotor / permanent magnet is in a positive rest position, within the valid range of its strength. H (-F H ) only generates an external magnetic field with a rise time T M can be easily detected based on

[0036] In order to take advantage of the results and findings given above, the stepper motor control circuit 20, in particular the circuit 24 for detecting the external magnetic field, and more particularly the circuit 36 ​​for processing the measured rise time, is arranged in a main embodiment to enable the implementation of a method for detecting an external magnetic field, the two main modes of which are illustrated in Figures 15 and 16, respectively.

[0037] FIG. 15 shows the steps of a variant of a first embodiment of a method for detecting an external magnetic field, in which the electrical detection pulse is in phase with the stationary position of the rotor, and FIG. 16 shows the steps of a variant of a second embodiment of a detection method according to the invention, in which the electrical detection pulse is in antiphase with the stationary position of the rotor.

[0038] In the first, "in-phase" detection mode, the detection method first determines the rest position of the permanent magnet. This information is generally known in the control circuit of the bipolar magnet stepper motor, since the electrical drive pulse should be in phase with the rest position of the permanent magnet. Then, an in-phase electrical detection pulse (detection pulse), for example of duration 1.5 ms to 2.0 ms, is generated. At the start of the detection pulse, the current I B The circuit that measures (t) is active and the reference current I Ref up to a value substantially equal to the value of B (t) Rise time T M At the beginning of the detection pulse, a timer 32 is triggered so that the rise time can be measured. In the above-mentioned variant, the reference current has an absolute reference value, for example 0.20 mA, chosen between 0.10 mA and 0.30 mA, preferably between 0.15 mA and 0.25 mA. Once the rise time has been measured, this information can be used to calculate the rise time for a given external magnetic field H Ext , more specifically, a predetermined external magnetic flux F having a predetermined directivity, i.e., a positive directivity when the detection pulse has a negative polarity, and a negative directivity when the detection pulse has a positive polarity. H must be processed to detect the presence of an external magnetic field that generates a magnetic field within the isthmus (which therefore passes through the isthmus).

[0039] Rise time T by the processing circuit 36 M Various variants are possible for the processing of . In the variant shown in FIG. 15, the processing circuit generates at least one magnetic flux F having a predetermined intensity in the isthmus 12a and 12b of the stator 4. H It is intended to detect an external magnetic field that generates

[0040] In the table of Figure 14, the external magnetic field HExt The values ​​of F are given for the specific case of an external magnetic field propagating parallel to the plane of the stator and approximately perpendicular to the alignment direction of the two isthmuses. In this specific case, the corresponding magnetic flux F, which is decisive for the detection method according to the invention, H 8 shows the relationship between these two physical variables for the considered example. In order to determine the external magnetic field of relatively high intensity, which is equivalent to the external magnetic field according to the specific case mentioned above having a value of more than 1,000 A / m, more specifically at least 1,200 A / m, with respect to the values ​​in the table of FIG. 14, the processing circuit 36 ​​determines the rise time T M is longer than a first reference duration, i.e. 0.9 ms in the considered example. If so, this first detection mode determines, for a positive rest position, that there is a negative external magnetic field with an intensity higher than the first minimum value, i.e. at least 1,200 A / m, for the aforementioned specific case, for an equivalent external magnetic field, or for a negative rest position, that there is a positive external magnetic field with an intensity higher than the second minimum value, i.e. at least 1,200 A / m, for the aforementioned specific case, for an equivalent external magnetic field, or for a negative rest position. If not, this first detection mode determines the opposite for the positive and negative rest positions.

[0041] In the second "opposite phase" detection mode, the detection method also first determines the rest position of the permanent magnet / rotor. Then, it generates detection pulses in opposite phase, for example with a duration between 1.5 ms and 2.0 ms. The reference current I Ref Current I B (t) Rise time T M Once the rise time is measured, this information can be used to calculate the Ext , more precisely, an external magnetic flux F having a given directionality, i.e. a positive directionality when the detection pulse has a negative polarity and a negative directionality when the detection pulse has a positive polarity. HIn the variant shown in FIG. 16, the processing circuitry is processed to detect a magnetic flux F having at least a given strength substantially equal to that selected in the first detection mode. H To this end, the processing circuit 36 ​​detects the external magnetic field that generates a rise time T M is shorter than a second reference duration, i.e. 0.55 ms in the considered example. If so, this second detection determines, as in the first detection mode, for the positive rest position, the presence of a negative external magnetic field having an intensity higher than a first minimum value, for the aforementioned case equal to an intensity of 1,200 A / m or for an equivalent external magnetic field with respect to the external magnetic flux generated at the two isthmuses of the stator, or for the negative rest position, the presence of a positive external magnetic field having an intensity higher than a second minimum value, for the equivalent external magnetic field or for the aforementioned specific case equal to an intensity of 1,200 A / m. If not, this second detection mode determines the opposite for the positive and negative rest positions.

[0042] Therefore, as already mentioned, a method for detecting an external magnetic field generating an external magnetic flux of a given intensity in the isthmus of the stator in the absence of any information about the directionality of the external magnetic flux in these isthmuses preferably comprises a first phase in which the rotor is in a positive or negative rest position according to the first or second detection mode, and a second phase in which the rotor is in a negative or positive rest position, respectively, also according to the first or second detection mode, in order to enable detection of this external magnetic field regardless of its directionality in these isthmuses.

[0043] Generally, the rise time T MThe circuit 36 ​​for processing is configured to be able to determine, at least within a range of valid values, whether the value / strength of the external magnetic field or its magnetic flux passing, if appropriate, through these two isthmuses according to a direction perpendicular to the alignment direction of these two isthmuses of the stator, or the value / strength of said external magnetic field or its magnetic flux passing, if appropriate, through these two isthmuses according to said direction, is higher than a reference value. The variants shown in figures 15 and 16 relate to the second case mentioned above. As for the first case mentioned above, the table of figure 14 can be calculated by performing a linear approximation between the two values ​​of the table to define an intermediate value, or by determining whether the rise time T M as a function of the external magnetic field H Ext This may be used by determining a function or curve that gives the values ​​of

[0044] In a particular variant, the circuitry processing the rise time is configured to be able to determine, at least within a range of valid values, whether the value of said external magnetic field or its magnetic flux passing appropriately through the two isthmuses according to the aforementioned directions is within a particular range of values ​​of a number of predetermined values ​​successive to one another.

[0045] In the aforementioned detection mode, the circuitry processing the rise time is configured so as to be able to determine also the direction of the external magnetic field passing appropriately through the two isthmuses according to the aforementioned directions.

[0046] In a first advantageous variant, the circuit for detecting the external magnetic field is configured to generate one or more detection pulses in opposite phase to the rotor's rest position, i.e. a negative electrical pulse when the rotor is in a positive rest position and a positive electrical pulse when the rotor is in a negative rest position, so that detection of an external magnetic field does not cause the rotor to advance one step, since the opposite phase electrical pulse is not a drive pulse.

[0047] In a second advantageous variant, the circuit for detecting the external magnetic field is configured to generate one or more detection pulses in phase with the rest position of the rotor, i.e. a positive electric pulse when the rotor is in a positive rest position and a negative electric pulse when the rotor is in a negative rest position, the in-phase electric pulses being configured to have a duration selected to allow detection of the external magnetic field, the selected duration being too short for the stepper motor to move forward one step.

Claims

1. In the electronic control circuit (20) of the stepping motor (2), The motor comprises a rotor (3) and a stator (4), the rotor (3) comprising bipolar permanent magnets (6) with magnetization axes perpendicular to the rotor axis of rotation (7), the stator (4) defining a magnetic circuit, an opening (8) forming a housing for the permanent magnets, two diametrically opposed isthmuses (12a and 12b) around the opening in a first direction (14) perpendicular to the axis of rotation, and two rest positions of the rotor in which the permanent magnets are oriented in both directions, respectively, in a second direction (16) angularly offset from the first direction, the permanent magnets being oriented in both directions in the two rest positions by a first magnetic flux (F Ａ ), a first rest position corresponds to a positive directionality of the first magnetic flux, and a second rest position corresponds to a negative directionality of the first magnetic flux, and the motor generates a positive electrical pulse (+I Ｂ (t)) or a negative electric pulse (-I Ｂ a coil (18) attached to the magnetic circuit so as to generate a second magnetic flux passing through the two isthmuses in each of the positive and negative directions when a second magnetic flux is applied to the magnetic circuit, the electronic control circuit comprising means for determining a rest position of the rotor from among the first and second rest positions, and an electric pulse generator (22) configured to selectively apply positive and negative electric pulses to the coil, The electronic control circuit (20) includes a circuit (24) for detecting an external magnetic field generated by a circuit (26) for measuring a current, and a circuit (26) for comparing the measured current with a reference current (I Ｒｅｆ ) and a circuit (28) for comparing the rise time (T) between the moment one of the electrical pulses is triggered and the next moment the current through the coil reaches the reference current. Ｍ A time measurement circuit (32) configured to measure the rise time, and a circuit (36) for processing the rise time, the measured rise time being proportional to an external magnetic field (H Ｅｘｔ and a circuit configured to determine whether a signal indicates the presence of a signal.

2. 2. The electronic control circuit according to claim 1, characterized in that the two isthmuses of the motor are arranged such that the first magnetic flux and the second magnetic flux pass through them mainly according to a third direction (40) perpendicular to the first direction.

3. The rise time (T Ｍ 2. The electronic control circuit according to claim 1, characterized in that the circuit (32) for processing the external magnetic field strength or the magnetic flux strength of the external magnetic field passing through the two isthmuses, as appropriate, is configured to be able to determine, at least approximately within a range of valid values, the strength of the external magnetic field or the strength of the magnetic flux strength of the external magnetic field passing through the two isthmuses, as appropriate, or whether the strength of the external magnetic field or the strength of the magnetic flux strength passing through the two isthmuses is greater than a predetermined minimum value.

4. The rise time (T Ｍ 4. The electronic control circuit according to claim 3, characterized in that the circuit for processing the external magnetic field strength or the magnetic flux strength passing through the two isthmuses, at least within a range of valid values, is configured to be able to determine whether the strength of the external magnetic field or the strength of the magnetic flux passing through the two isthmuses, as appropriate, is within a specific value range of a plurality of specific value ranges consecutive to one another.

5. The electronic control circuit according to any one of claims 1 to 4, characterized in that the circuit (24) for detecting the external magnetic field is configured so as to be able to determine the directionality of the external magnetic field passing appropriately through the two isthmuses.

6. 5. An electronic control circuit according to claim 1, configured to generate an electric pulse in antiphase with the rest position of the rotor, i.e. a negative electric pulse when the rotor is in the positive rest position and a positive electric pulse when the rotor is in the negative rest position, in order to detect the presence of an external magnetic field, whereby detection of the external magnetic field does not cause the rotor to move forward one step.

7. configured to generate an electrical pulse in phase with the rest position of the rotor, i.e. a positive electrical pulse when the rotor is in the positive rest position and a negative electrical pulse when the rotor is in the negative rest position, in order to detect the presence of an external magnetic field; 5. An electronic control circuit according to claim 1, wherein the in-phase pulses have a duration selected to enable detection of the external magnetic field, the selected duration not causing the stepper motor to advance one step.

8. A clock movement comprising an electronic control circuit (20) according to any one of claims 1 to 4 and a stepping motor (2), The motor comprises a rotor (3) and a stator (4), the rotor (3) comprising bipolar permanent magnets (6) with magnetization axes perpendicular to the rotor axis of rotation (7), the stator (4) defining a magnetic circuit, an opening (8) forming a housing for the permanent magnets, two diametrically opposed isthmuses (12a and 12b) around the opening in a first direction (14) perpendicular to the axis of rotation, and two rest positions of the rotor in which the permanent magnets are oriented in both directions, respectively, in a second direction (16) angularly offset from the first direction, the permanent magnets being oriented in both directions in the two rest positions by a first magnetic flux (F Ａ ), a first rest position corresponds to a positive directionality of the first magnetic flux, and a second rest position corresponds to a negative directionality of the first magnetic flux, and the motor generates a positive electrical pulse (+I Ｂ (t)) or a negative electric pulse (-I Ｂ a coil (18) attached to the magnetic circuit so as to generate a second magnetic flux passing through the two isthmuses in each of the positive and negative directions when a second magnetic flux (t) is supplied to the magnetic circuit.

9. A wristwatch comprising a clock movement according to claim 8.

10. A method for detecting an external magnetic field in which a stepping motor (2), in particular a timepiece motor, controlled by an electronic control circuit (20) according to any one of claims 1 to 4 is arranged, comprising: determining the rest position of the rotor (3), i.e. whether the rotor is in a positive or negative rest position; Electrical detection pulse (I Ｂ (t) determining whether the rise time is longer than a first reference time duration if the polarity of the electrical pulse is in phase with the stationary position of the rotor, and determining whether the rise time is shorter than a second reference time duration if the polarity of the electrical detection pulse is out of phase with the stationary position of the rotor; If the polarity of the electric pulse is negative and the rise time satisfies one of the two conditions in the previous step, an external magnetic field (H Ｅｘｔ determining the presence of an external magnetic field having a negative directionality and an intensity higher than a given predetermined second minimum value if the rest position of the rotor is positive and the rise time satisfies one of the two conditions of the previous step; A method comprising:

11. 11. A method according to claim 10, characterized in that it comprises a first phase in which the aforementioned steps are performed when the rotor is in a positive or negative rest position, and a second phase which occurs after the motor has performed one motor step and in which the aforementioned steps are performed again while the rotor is in a negative or positive rest position, respectively.

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