HK1237863B - Position sensor for a timepiece setting stem - Google Patents

Description

Position sensor for timepiece setting lever

Technical Field

The present invention relates to the field of sensing the position and/or movement of a rotatable setting stem of a timepiece. More particularly, but not exclusively, the present invention relates to a capacitive sensor arrangement suitable for sensing the movement and/or position of a setting stem of a timepiece.

Background Art

In devices that combine mechanical moving parts and electronic control circuits, such as electromechanical timepieces, accurate sensors are needed to sense the position and/or movement of the rotating mechanical parts. For watches with a rotatable setting lever, for example, accurate and responsive sensors are needed to detect the instantaneous angular position and/or rotation of the setting lever so that the wearer's preferences can be quickly and accurately converted into electronic information used by the watch's electronic control system. In the field of wearable timepieces, it is important to maximize the accuracy and speed of such sensors while minimizing power consumption. In addition, the small size of components such as the setting lever of a watch means that the rotation/motion sensor must be able to detect small movements of tiny objects, such as the rotation of a setting lever with a diameter of one millimeter or even less. The sensor component must also be small because space is limited. Such a sensor should preferably be contactless in order to reduce wear and thereby extend the service life of the timepiece. The sensor component should also be easy to manufacture.

Existing technology

A non-contact sensor has been proposed in US Patent No. 6,252,825, which describes the use of a capacitive sensor for detecting the position and/or movement of a setting lever of a timepiece. The setting lever is provided with a rotor electrode shaped to facilitate adjustment of the capacitance between two stator electrodes. An embodiment is also described in which two such capacitors are arranged orthogonally, allowing a sensor control system to infer the direction of rotation of the setting lever.

Summary of the Invention

An object of the present invention is to provide a capacitive sensor for determining the instantaneous angular position of a rotatable element of a timepiece, the capacitive sensor comprising a plurality of stator electrodes and at least one rotor electrode arranged to rotate with the rotatable element, wherein the at least one rotor electrode and the stator electrode are arranged to provide a capacitance between each of the plurality of stator electrodes during a rotation cycle of the rotatable element, such that each of the capacitances varies over at least a portion of the rotation cycle due to the influence of the one rotor electrode, and wherein: the at least one rotor electrode comprises a first rotor electrode and a second rotor electrode; the capacitance comprises a first differential capacitance pair comprising a first capacitance formed between a first stator electrode and a second stator electrode of the stator electrodes during a first portion of the rotation cycle, and a second capacitance formed between the second stator electrode and a third stator electrode of the stator electrodes during a second portion of the rotation cycle, the first capacitance having a first instantaneous capacitance value _X1 , and the second capacitance having a second instantaneous capacitance value _X2 and the capacitance includes a second differential capacitance pair, the second differential capacitance pair including a third capacitance formed between a fourth stator electrode and a fifth stator electrode during a third portion of the rotation cycle, and a fourth capacitance formed between the fifth stator electrode and a sixth stator electrode during a fourth portion of the rotation cycle, the third capacitance having a third instantaneous capacitance value X ₃ , and the fourth capacitance having a fourth instantaneous capacitance value X ₄ . The capacitance values X ₁ , X ₂ , X ₃ , and X ₄ vary depending on the angular positioning of the first and second rotor electrodes.

The proposed new solution enables a more precise measurement of the position and/or movement of a rotatable element, thereby providing a finer resolution, without requiring a greater number of rotor and/or stator electrodes of the sensor.

The use of differential capacitance values for determining angular position further improves the capacitive sensor's immunity to external influences, such as parasitic capacitance or variations due to humidity or temperature changes, and thus increases its measurement accuracy. According to a preferred embodiment of the invention, the rotor electrodes are made of two identical parts extending diametrically on either side around their axis of rotation, so that the position can be determined with an accuracy of only +/- 180 degrees. Thus, only incremental sensors are provided for measuring angular displacement or angular velocity, but not absolute angular position.

According to a variant of the invention, the first and second rotor electrodes and the first, second, third, fourth, fifth and sixth stator electrodes are configured so that capacitance values of _C1 , _C2 , _C3 and _C4 can be sensed between the first and second, second and third, fourth and fifth, and fifth and sixth stator electrodes, respectively.

According to another variant of the invention, the capacitive sensor comprises a sensor driver circuit for sensing capacitance values _X1 , _X2 , _X3 and _X4 of capacitances _C1 , _C2 , _C3 and _C4 , respectively, and for determining angular position and/or displacement by evaluating a first differential capacitance value _X1-2 = _X1 - _X2 and a second differential capacitance value _X3-4 = _X3 - _X4 .

According to another variant of the invention, the first and second differential capacitance pairs are arranged such that _X1-2 varies as a first function of the rotational position of the rotatable element and _X3-4 varies as a second function of the rotational position of the rotatable element.

According to another variant of the invention, the first and/or second function is substantially a sine curve or a cosine curve having a period of 180°.

According to another variant of the invention, the second function has the same form as the first function, but is phase-shifted by a phase shift angle in the rotation cycle relative to the first function.

According to another variant of the invention, the phase shift angle is substantially 45 degrees, +/- 90 degrees, which allows the rotational position of the rotatable element to be derived with the aid of trigonometric formulas.

According to another variant of the invention, the first, second and third, and/or fourth, fifth and sixth stator electrodes are arranged in a common plane orthogonal to the axis of rotation of the rotatable element. This allows simplifying the manufacturing process and improving the compactness of the provided sensor device.

According to another variant of the invention, the first rotor electrode and/or the second rotor electrode are formed in an axial end face of the rotatable element. Preferably, the first and second rotor electrodes are also formed on the same plane in order to simplify machining.

According to another variant of the invention, the first, second and third, and/or fourth, fifth and sixth stator electrodes are arranged adjacent to the outer circumference of the rotatable element.

According to another variant of the invention, the first rotor electrode and/or the second rotor electrode are formed in or on the outer circumferential surface of the rotatable element.

According to another variant of the invention, the capacitive sensor comprises a stator element comprising a plurality of angular stator electrode regions arranged about a rotation axis of the rotatable element, wherein a first differential capacitance pair is located in a first angular stator electrode region of the angular stator electrode regions and a second differential capacitance pair is located in a second angular stator electrode region of the angular stator electrode regions, the second angular stator electrode region being angularly shifted relative to the first angular stator electrode region by a phase shift angle.

According to another variant of the invention, the capacitive sensor comprises a rotor element comprising a plurality of angular rotor electrode regions arranged about the rotation axis of the rotatable element, wherein the first rotor electrode comprises a first angular rotor electrode region of the angular rotor electrode regions and the second rotor electrode comprises a second angular rotor electrode region of the angular rotor electrode regions, the first angular rotor electrode region extending over a larger angular sector than the second angular rotor electrode region.

According to another variant of the invention, the rotatable element is assembled to the distal end of a setting stem of the timepiece.

The present invention also aims to provide a sensor computing unit for a capacitive sensor as described above, the sensor computing unit being configured to determine the instantaneous angular orientation of a rotatable element comprising two rotor electrodes by:

Determining a first instantaneous differential value (X _1-2 ) between the first capacitor C ₁ and the second capacitor C ₂ , and a second instantaneous differential value (X _3-4 ) between the third capacitor C ₃ and the fourth capacitor C ₄ ;

identifying a first plurality of plausible values of the first function corresponding to the first differential instantaneous value (X _1-2 ) using predetermined correspondence information of the first function;

identifying a second plurality of reasonable values of the second function corresponding to the second differential instantaneous value (X _3-4 ) using predetermined correspondence information of the second function; and

wherein the second plurality of plausible values is a pair of angular values that are 180° apart and correspond to the angular positions of the two rotor poles, and

An angular value between the pair of second plurality of plausible values that is closest to the last previously calculated angular position is selected as the instantaneous angular position.

The maximum rotational speed determines the maximum time between two measurements. If the initial value is chosen arbitrarily, the position is limited to a range of 180°, which is sufficient for most watch applications, where absolute angular positioning is not required, but only incremental detection. If absolute position is required, another sensor with one pulse every 360° should preferably be added, or the structure of the rotor electrode pairs should be modified to enable each to be distinguished relative to the other.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent from the following description of non-limiting exemplary embodiments described with reference to the accompanying drawings, in which:

- FIG. 1 shows, in an isometric schematic view, an example of a capacitive sensor assembly for a setting lever of a timepiece according to the invention;

- FIG. 2 shows in isometric schematic form a rotor electrode arrangement used in the example capacitive sensor assembly shown in FIG. 1 ;

- FIG3 shows in schematic plan view a stator electrode arrangement used in the example capacitive sensor assembly shown in FIG1 ;

- FIG. 4 shows an end view of a rotor electrode used in the example capacitive sensor assembly shown in FIG. 1 ;

- FIG5 illustrates the angle and capacitance of the example capacitive sensor assembly of FIG1 relative to the stator electrodes;

- FIG. 6 illustrates angles associated with rotor electrodes used in the example capacitive sensor assembly shown in FIG. 1 ;

FIG. 7 graphically illustrates how the difference between two differential capacitance pairs in the example capacitive sensor of FIG. 1 varies during a rotation cycle;

- FIG8 shows a perspective view of an alternative embodiment of a capacitive sensor assembly according to the invention, in which the stator electrodes are arranged on a flexible substrate wrapped around a rotatable element;

- FIG. 9 shows a detailed perspective view of a series of capacitors mounted parallel to the stator electrodes of FIG. 8 ;

- FIG10 shows a cross-sectional view of the rotor and stator electrodes in a plane perpendicular to the axis of rotation of the rotatable element of FIG8 ;

- Figure 11 shows an alternative form of rotatable element applicable to the present invention.

DETAILED DESCRIPTION

The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The same or corresponding functional and structural elements appearing in different drawings are assigned the same reference numerals.

FIG1 shows an example of a rotatable element such as a pinion shaft or a setting lever that can be found in a timepiece. In the example embodiments described below, the setting lever of a watch will serve as an illustrative example of the application of the capacitive sensor of the present invention. The setting lever may also be referred to as a crown lever. Note that the setting lever itself is not shown in FIG1 . The rotatable element 3 is rotatable about an axis of rotation 4 and is provided with an engaging part (in this example a groove 8) for engaging with a corresponding part of the setting lever. The engaging part in this example is designed to cooperate with the setting lever so that the setting lever can be moved axially along the axis of rotation 4 without causing any axial movement of the rotatable element 3, but so that any rotational movement of the setting lever is converted into rotational movement of the rotatable element 3.

The rotatable element 3 shown in FIG1 is provided with one or more rotor electrodes 5 at its distal end. In this example, there are two rotor electrodes arranged diametrically opposite each other with respect to the axis of rotation 4. The rotor electrodes 5 are substantially flat and are arranged to face a plurality of stator electrodes, which are similarly flat and coplanar with the rotor electrodes and are separated from the rotor electrodes by a thin dielectric, which may be, for example, an air gap or a piece of solid dielectric material such as a plastic film. The stator electrodes may advantageously be formed as tracks on a printed circuit board (PCB) 10, for example, and, for reasons to be described later, are arranged to form two differential capacitor pairs indicated by arrows 1 and 2. The PCB 10 may also carry sensor driver circuitry 9 for providing an electrical interface to the differential capacitor pairs 1 and 2.

In the case of a watch, the dimensions of the various elements shown in Figure 1 will be tiny. For example, the diameter of the rotatable element 3 may be 1 mm or less, and the PCB 10 may have an area of five or six square millimeters or less.

FIG2 shows a different view of the rotatable element 3 shown in FIG1 . This view shows the shape of the two electrodes 5a and 5b, which can be formed by milling two shoulders 6 in the peripheral surface at the end of the rotatable element 3. The end face of the rotatable element 3 can also include a spacer element 7 for providing physical contact with the PCB 10 and thus maintaining a constant spacing from the PCB 10. This rotatable element 3 with the groove 8, the spacer element 7 and the shoulder 6 can be easily manufactured from metal using standard machine tool technology even when its dimensions are small. For the rotatable element 3 used for the setting lever of a watch, the spacer element 7 has a thickness generally included between 0.05 mm and 0.15 mm and allows for greater shock resistance.

FIG3 illustrates how the stator electrodes are arranged to form two differential capacitance pairs 1 and 2 in capacitive proximity to the rotor electrodes. FIG3 shows six stator electrode regions 11, 12, 13, 21, 22, and 23 (areas shaded with left-angled shading), each of which, in this example, is formed as part of a metal track of a PCB 10. Each of the metal tracks also includes connector pads 11′, 12′, 13′, 21′, 22′, 23′ (shaded with right-angled shading) for connecting each of the corresponding stator electrodes 11, 12, 13, 21, 22, and 23 to the sensor drive circuit 9. The stator electrodes 11, 12, 13, 21, 22, and 23 are formed as concentric arc segments centered on the rotation axis 4 of the rotatable element 3 so that the capacitance values are modeled as a sine or cosine function depending on the angular position of the rotatable element 3 on which the rotor electrodes are arranged, as further described below with reference to FIG5-7. This is just one example of a configuration of stator electrodes that can be used to implement the present invention. Other configurations of stator and rotor electrodes are possible, which can be arranged around the periphery of the rotatable element 3 rather than (or also) being orthogonal to the axis of rotation 4 as in the example shown. Figures 8-11 show an alternative embodiment of the present invention in which the rotatable element 3 is divided into two parts and the stator electrodes are arranged on a flexible substrate wrapped around its periphery, as described below.

In the example shown in FIG3 , the first differential capacitance pair 1 includes first, second, and third stator electrode regions 11, 12, and 13 (shaded with left-slashed shading), while the second differential capacitance pair 2 includes similarly shaded fourth, fifth, and sixth stator electrode regions 21, 22, and 23. When the rotor electrode faces two of the stator electrodes (e.g., the first and second stator electrodes 11 and 12) in capacitive proximity to form a first pair of stator electrodes, capacitance is generated between the stator electrodes 11 and 12 via the rotor electrode. FIG4 shows an example of a rotor electrode arrangement designed to face the stator electrodes shown in FIG3 , thereby generating a varying capacitance between the stator electrode pair as the rotatable element 3 rotates. The rotor electrode regions 5a and 5b are shaded to indicate which areas of the axial end surface of the rotating element 3 are capacitively close to the stator electrodes 11, 12, 13, 21, 22, and 23, which respectively form a first pair of stator electrodes between the first stator electrode 11 and the second stator electrode 12, a second pair of stator electrodes between the second stator electrode and the third stator electrode, a third pair of stator electrodes between the fourth stator electrode 21 and the fifth stator electrode 22, and a fourth pair of stator electrodes between the fifth stator electrode 22 and the sixth stator electrode 23. These rotor electrode regions 5a and 5b are notional regions and are not necessarily made of a different material from the surrounding rotatable element 3. The rotatable element 3 may, for example, be machined from a single, continuous piece of metal or other conductive material, or manufactured in other ways.

In the example shown, rotor electrodes 5a and 5b are preferably electrically connected to the same ground potential as the metal case or movement plate. Consequently, there is no need for isolation between the case and the rotating elements, which is advantageous, as such isolation would be difficult to achieve in a small package. In this case, rotor electrodes 5a and 5b play a passive role in the capacitance, allowing the capacitance to be measured at the connections 11', 12', 13', 21', 22', 23' to stator electrodes 11, 12, 13, 21, 22, and 23.

Figures 5 and 6 show the same arrangement of stator and rotor electrodes as in Figures 3 and 4, but with the angles and capacitances indicated schematically. _X1 represents the instantaneous value of capacitance _C1 , measurable between the first and second stator electrodes 11 and 12. _X1 has a maximum value (referred to as zero for simplicity) when neither rotor electrode 5a or 5b covers the first stator electrode 11 (i.e., no portion of angular sectors _α5a or _α5b lies between _α7 and _α0 ), and has a minimum value when either rotor electrode 5a or 5b completely covers the first stator electrode ₁₁ (i.e., when angular sectors _α5a or _α5b completely encompass the angle between _α7 and _α0 ), i.e., when the dielectric between the two stator electrodes, whose isolation properties are affected by the rotor, is minimal. When either rotor pole 5a or 5b partially covers the first stator electrode 11 (i.e., when angular sector _α5a or _α5b partially coincides with the angle between _α7 and _α0 ), _X1 has an intermediate value. Angular positions _α0 , _α1 , α2, _α3 , _α4 , _α5 , _α6 , and _α7 each indicate the delimitation of stator electrodes 11, 12, ₁₃ , 21, 22, and 23 (i.e., the start or end of rotation relative to the rotatable element 3), and may be evenly distributed about the axis of rotation 4, defining eight angular sectors of 45 degrees each. The angular sectors _α5a and _α5b of each of the rotor electrodes 5a and 5b can advantageously be arranged to angularly span two adjacent segments defined by the angular positions _α0 , _α1 , _α2 , _α3 , _α4 , _α5 , _α6 , and _α7 , i.e., approximately 90 degrees in this case. During clockwise rotation of the rotatable element 3 (clockwise relative to the stator electrodes in Figures 3 and 5), each rotor electrode 5a and 5b produces a substantially uninterrupted variation of the finite capacitance values X1, X2, X3, and X4 for each capacitance C1, C2, C3, and C4 as the corresponding rotor electrode 5a or 5b sweeps through successive pairs of stator electrodes ₁₁ and ₁₂ (i.e., the first pair); ₁₂ and 13 (i.e., the second pair); ₂₁ and ₂₂ (i.e., the third pair); and finally ₂₂ and ₂₃ (i.e., the _fourth pair). 6 indicates a centerline in the middle of the two rotor poles 5a and 5b, which will be used as a reference when describing how the values of _C1 , _C2 , _C3 and _C4 vary during rotation of the rotatable element 3. This centerline 14 helps define the instantaneous angular position α _R of the rotatable element 3.

FIG7 illustrates how each _{of the} capacitance values _X1 , _X2 , _X3 , and X4 varies with the angular position α of the rotatable element 3 during such a clockwise rotation as the centerline 14 of the rotatable element 3 successively sweeps through the angular positions α0, α1, _α2 , _α3 , _α4 , α5, _α6 , and _α7 . FIG7 also illustrates how the differences _X1 -X2 and X3- _X4 vary during the same clockwise rotation of the rotatable element 3 through the angular positions _α0 , _α1 , _α2 , _α3 , _α4 , _α5 , _{α6 ,} and _{α7 .} FIG7 also illustrates an example of how the angular position _of the rotatable element 3 can be inferred from the instantaneous differences _X1 - _X2 between _the capacitances _C1 and _C2 and _X3 - _X4 between the capacitances _C3 and _C4 . In the example shown, the instantaneous measured values _{of X1-X2 and} X3 _{- X4} are _X1-2 and _X3-4 , respectively. The quantities _X1 - _X2 vary with the angular position α according to a first function, and the quantities _X3 - _X4 vary with the angular position α according to a second function. The stator and rotor poles can be arranged so that the second function is similar to the first function, but shifted by a predetermined phase shift angle. In the example shown in the previous Figures 1-6, as can be seen when comparing the values of _X1 - _X2 with the values of _X3 - _X4 in Figure 7, the phase shift angle was selected to be substantially 135 degrees. In fact, when considering all angles _α0 , _α1 , _α2 , _α3 , _α4 , _α5 , _α6 , and _α7 as multiples of 45 degrees, it can be understood that the following equation is satisfied:

X ₁ -X ₂ (α)＝X ₃ -X ₄ (α+135)

As shown in Figures 1-6 according to a preferred embodiment, the stator and rotor poles can be arranged so that the first and second functions can be approximated by sine or cosine functions. In this case, assuming the function _X3 - _X4 (α)=cos(2α), the above equations yield:

X ₁ -X ₂ (2α)=cos[2(α+135)]=cos[2α+270]=cos[2α-90]=sin(2α), and therefore

X ₁ -X ₂ /X ₃ -X ₄ =tan(2α),

This allows the instantaneous angular position α of the rotatable element 3 to be derived according to:

α=Arctan(X _1-2 /X _3-4 )/2,

where alpha (α) is a value between +/- 90°.

From the above formulas and equations it can be understood that a second possible absolute value of α is α+/-180°, which means that the sensor cannot distinguish between two symmetrical positions of the rotor electrodes, where the positions 5a and 5b of the two rotor electrodes are opposite.

In fact, instead of a phase shift of 135 degrees, any phase shift of 45 degrees plus or minus 90 degrees can be applied without significantly changing the contents of the trigonometric formulas. In fact, it can be understood that applying a phase shift of 45 degrees instead of 135 only changes the sign of the function _X3 - _X4 (α), since

cos[2(α+45)]=cos[2α+90]=-sin(2α)

In the case of other configurations of stator and rotor elements, other mathematical functions can be used to determine the angular position α from the measured values _X1-2 and _X3-4 , but with less computational simplicity. It will be understood that according to the preferred embodiment described above, the angular resolution of the sensor is in any case much better than the angular resolution in each angular sector of the stator electrodes (i.e., 45 degrees).

Alternatively, when the first and second functions cannot be approximated by a sinusoidal approximation of a cosine function, for example, to simplify the manufacture of the rotor poles, the value of the angular position α can be related to the values _X1-2 and _X3-4 by a lookup table of corresponding data or other corresponding information sources, as explained further below with reference to the bottom portion of FIG. 7 . The form of the first and second functions more generally depends on the shape of the rotor poles (e.g., the angular sector values _α5a or _α5b ) and the dimensions of the stator poles (e.g., when considering _α0 and _α7 as boundary angular positions and also on their radii). As can be understood from the _X1 - _X2 graph, at a given instant in time, for a given measured value _X1-2 of the first differential capacitance pair 1, there are four possible values _αA , _αB , _αC , and _αD for the angular position α of the rotatable element 3. Therein, for a measurement made at the same instant as the value _X1-2 , only the angular positions _αB and _αD correspond to the values of _αE and _αF of _X3 - _X4 (at points E and F) that are reasonable considering the value _X3-4 of _X3 - _X4 of the second differential capacitance pair 2.

This allows the actual angular position pair _αE and _αF to be derived from the angular position of the two symmetrically arranged rotor poles 5a and 5b. The two angles _αE and _αF of this pair are separated by 180 degrees because they actually correspond to two possible angles between each pole 5a and 5b extending along the center line 14 shown in FIG6. At the bottom of FIG7, it can be understood that there is a slight offset between _αB and _αE , while _αD and _αF are exactly the same. This only shows that the modeling is imperfect compared to the sine/cosine function, but does not help to distinguish between the two possible values to determine the actual instantaneous angular position _αR of the rotatable element.

Due to the symmetrical arrangement of the rotor poles 5a, 5b, and when the sensor is used for incremental detection, the first instantaneous angular position _αR can be arbitrarily selected between the two possible values of the actual angular position pair _αE and _αF . However, once this first angular position has been set, the instantaneous angular position _αR is preferably defined recursively by selecting the one of the two possible angular values of the angular position pair _αE and _αF that is closest to the last calculated instantaneous angular position _αR . From an empirical and statistical point of view, this corresponds to the most likely position, taking into account the last measured value. In FIG. 7 , this desired angular position results in _αF .

As long as the angular velocity remains below the upper limit set by the system, the angular displacement can then be easily calculated by calculating the difference between the instantaneous angular position α _R and the last calculated instantaneous angular position, which produces an angle comprised between -90° and 90°. This limit may depend, among other things, on the frequency of the measurement. The direction of rotation is then simply indicated by the sign of this difference angle.

The maximum permissible rotational speed determines the maximum time between two measurements. This measurement rate is proportional to the number of rotor poles. With an ideal absolute sensor, the measurement rate can be half that of the variant with two rotor poles. The goal is to measure an angular displacement of several revolutions (>>360°) during a time interval. The rotational speed and direction can be easily calculated from the angular displacement.

With standard digital incremental sensors, the number of rotor poles (e.g., teeth) must be much higher than two, as in the framework of the proposed solution, in order to achieve the same resolution. Due to the small available volume, such a small number of teeth is not possible. Consequently, the proposed incremental sensor allows solving this technical problem by significantly increasing the angular resolution without simultaneously increasing the number of rotor poles.

However, it should be understood that the preferred calculation method described above is only one of the possible methods that can be used to infer the actual angular position from the measured value of the capacitance. The calculation can be performed by appropriate circuitry and/or software in the sensor driver circuit 9 on the PCB 10, or by a separate processor unit. The above example configuration including two rotor electrodes and two differential capacitor pairs is also only one of the possible configurations for implementing the present invention. Other numbers of rotors and/or static electrodes, and/or other relative angles between the electrodes can be used.

The following Figures 8 to 11 described below show an alternative embodiment of the invention in which the stator electrodes are no longer arranged on the same plane of the PCB 10, but on a flexible substrate 100 around which the rotatable element 3 is wound, i.e., here mounted at the end of the hour hand 30. The rotatable element 3 itself is divided into two distinct sub-pieces, namely a first sub-rotor 31 and a second sub-rotor 32, separated by a slot 80 in which a fixing element (not shown) can be housed to allow precise axial positioning along the axis of rotation 4.

As can be understood from FIG9 , the stator electrodes are arranged according to an array pattern, which shows:

- a central row R comprising four thick electrodes R1, R2, R3 and R4, and

- Two lateral rows, namely a first lateral row L and a second lateral row L', each of which comprises four thinner electrodes (ie L1 , L2, L3, L4 and L1 ', L2', L3' and L4' respectively).

As can be understood from FIG8 , the first sub-rotor 31 is configured to fill the gap between the first lateral row L of stator electrodes and the central row R of electrodes, while the second sub-rotor 32 is configured to fill the gap between the second lateral row L' of stator electrodes and the central electrode R. Therefore, the capacitance value between the first electrodes of the first lateral row L1 and the first central electrode R1 (forming a first pair of stator electrodes) changes depending on the angular position of the first sub-rotor 31 during its rotational cycle, while the capacitance value between the first electrodes of the second lateral row L1' and the first central electrode R1 (forming another first pair of stator electrodes) changes depending on the angular position of the second sub-rotor 32 during its rotational cycle. The same applies to each of the second, third, and fourth pairs of electrodes formed by the stator electrodes L2-R2 and L2'-R2, L3-R3 and L3'-R3, and L4-R4 and L4'-R4, respectively. The fact that two rotatable elements are available instead of a single rotatable element, as shown in the previous embodiments of Figures 1-5, also allows doubling the capacitance value X1, X2, X3, X4 of each capacitor C1, C2, C3 and C4 formed between two series of stator electrodes, since, for example, in the case where the wiring pattern starts from a central row R, having two side rows L, L' on either side of the central row R allows having two capacities branched in parallel.

As shown in FIG. 9 , which illustrates a cross-section through either the plane of the first sub-rotor 31 or the second sub-rotor 32 , the functional principle of this alternative embodiment for generating angular values is otherwise very similar to that of the previous preferred embodiment shown in FIGS. 1-5 , since the angular displacement between the first and second capacitors C1, C2 remains 90 degrees, while the angular displacement between the first and third capacitors C3 is now only 45 degrees, instead of 135 degrees as in FIG. As previously mentioned, while sinusoidal modeling can be used to derive the actual angular position of the rotor, it only affects the sign of the function. Nevertheless, the first differential capacitance pair 1 formed by the first and second capacitors C1 and C2, respectively, and the second differential capacitance pair 2 formed by the third and fourth capacitors, respectively, allow the angular position of the rotatable element 3 to be derived. Compared to the previous embodiment of FIG. 5 , these differential capacitance pairs now consist solely of interlocking capacitances.

The geometry of the rotatable element 3, which determines the waveform of the output signal of the capacitance value, is preferably selected so as to cover approximately two adjacent angular sectors—here, the stator poles corresponding to capacitors C2 and C4, each extending 45 degrees—and to leave the other two—here, capacitors C1 and C3—uncovered. However, as a variant embodiment shown in FIG10 , an elliptical shape is also conceivable without significantly compromising the sinusoidal modeling of the capacitance value. In any case, calculations based on the corresponding data lookup in the table remain feasible, and therefore, shapes that are easy to manufacture (such as the one in FIG10 ) can be selected for mass production.

Claims (12)

1. A capacitive sensor for determining the instantaneous angular position ( _αR ) of a rotatable element (3) of a timepiece, said capacitive sensor comprising: - Six stator electrodes (11, 12, 13, 21, 22, 23) are formed as concentric arc segments centered on the rotation axis of the rotatable element. The first stator electrode (11), the third stator electrode (13), the fourth stator electrode (21), and the sixth stator electrode (23) extend along 45°, while the second stator electrode (12) and the fifth stator electrode (22) extend along 135°. The first stator electrode (11) and the second stator electrode (12), the second stator electrode (12) and the third stator electrode (13), the fourth stator electrode (21) and the fifth stator electrode (22), and the fifth stator electrode (22) and the sixth stator electrode (23) each extend along a common 45-degree angle portion, and the four 45-degree angle portions are not identical. - A rotor electrode (5a, 5b) arranged to rotate together with the rotatable element (3), the rotor electrode consisting of two identical portions (5a, 5b) extending symmetrically along 90° on either side of its rotation axis, the two identical portions comprising a first rotor electrode portion (5a) and a second rotor electrode portion (5b). The rotor electrodes (5a, 5b) and the stator electrodes (11, 12, 13, 21, 22, 23) are arranged such that during the rotational cycle of the rotatable element (3), a capacitance (C1, _C2 , _C3 , _C4 ) is provided between two of the six stator electrodes ( ₁₁ , 12, 13, 21, ₂₂ , 23), such that each of the capacitances ( _C1 , C2, _C3 , _C4 ) varies at least for a portion of the rotational cycle due to the influence of the rotor electrodes (5a, 5b). The capacitors ( _C1 , _C2 , _C3 , _C4 ) include a first differential capacitor pair (1), which includes a first capacitor (C1) formed between the first stator electrode (11) and the second stator electrode (12) and a second capacitor ( _C2 ) formed between the second stator electrode (12) and the third stator electrode ( ₁₃ ). Depending on the angular positioning of the rotor electrodes (5a, 5b), the first capacitor ( _C1 ) has an instantaneous first capacitance value _X1 and the second capacitor ( _C2 ) has an instantaneous second capacitance value _X2 . The capacitors ( _C1 , _C2 , _C3 , _C4 ) include a second differential capacitor pair (2), which includes a third capacitor (C3) formed between the fourth stator electrode (21) and the fifth stator electrode (22) and a fourth capacitor ( _C4 ) formed between the fifth stator electrode (22) and the sixth stator electrode ( ₂₃ ). Depending on the angular positioning of the rotor electrodes (5a, 5b), the third capacitor ( _C3 ) has an instantaneous third capacitance value _X3 and the fourth capacitor ( _C4 ) has an instantaneous fourth capacitance value _X4 . The capacitive sensor includes a sensor driving circuit (9) for sensing capacitance values _X1 , _X2 , _X3 and _X4 , and for determining the instantaneous angular position ( _αR ) by evaluating a first differential capacitance value _X1-2 = _X1 - _X2 and a second differential capacitance value _X3-4 = _X3 - _X4 . 2. The capacitive sensor according to claim 1, wherein the first differential capacitor pair (1) and the second differential capacitor pair (2) are arranged such that the first differential capacitance value _X1-2 varies as a first function of the instantaneous angular position ( _αR ) of the rotatable element (3), and the second differential capacitance value _X3-4 varies as a second function of the instantaneous angular position ( _αR ) of the rotatable element (3). 3. The capacitive sensor according to claim 2, wherein the first and/or second function is a sine curve or a cosine curve with a period of 180°. 4. The capacitive sensor according to claim 2, wherein the second function has the same form as the first function and is phase-shifted by a phase shift angle relative to the first function in the rotation cycle. 5. The capacitive sensor according to claim 4, wherein the phase shift angle is 135 degrees or 45 degrees. 6. The capacitive sensor according to claim 1, wherein the first stator electrode (11), the second stator electrode (12) and the third stator electrode (13), and/or the fourth stator electrode (21), the fifth stator electrode (22) and the sixth stator electrode (23) are arranged in a common plane orthogonal to the rotation axis (4) of the rotatable element (3). 7. The capacitive sensor according to claim 1, wherein the first rotor electrode portion (5a) and/or the second rotor electrode portion (5b) are formed in the axial end face of the rotatable element (3). 8. The capacitive sensor according to claim 1, wherein the first stator electrode (11), the second stator electrode (12) and the third stator electrode (13), and/or the fourth stator electrode (21), the fifth stator electrode (22) and the sixth stator electrode (23) are arranged adjacent to the outer peripheral surface of the rotatable element (3). 9. The capacitive sensor according to claim 8, wherein the first rotor electrode portion (5a) and/or the second rotor electrode portion (5b) are formed in or on the outer peripheral surface of the rotatable element (3). 10. The capacitive sensor according to claim 4, comprising a stator element (10) including a plurality of corner stator electrode regions arranged about the rotation axis (4) of the rotatable element (3), wherein a first differential capacitor pair (1) is located in a first corner stator electrode region of the corner stator electrode regions, and a second differential capacitor pair (2) is located in a second corner stator electrode region of the corner stator electrode regions, the second corner stator electrode region being angularly displaced from the first corner stator electrode region by the phase shift angle. 11. The capacitive sensor according to claim 1, wherein the rotatable element (3) is arranged to be mounted to the setting rod of the timepiece. 12. The capacitive sensor according to claim 2, wherein the sensor driving circuit (9) is configured to determine the instantaneous angular position ( _αR ) of the rotatable element (3) by: Determine the first differential capacitance value _X1-2 = _X1 - X2, the first instantaneous differential value ( _X1-2 ), between the first capacitor ( _C1 ) and the second capacitor ( _C2 ), and the second differential capacitance value _X3-4 = _X3 - _{X4, the second instantaneous differential value (X3-4), between the third capacitor (C3 ) and} the _fourth capacitor ( _C4 ). Using the predetermined correspondence information of the first function, identify the first plurality of reasonable values ( _αA , _αB , _αC , _αD ) of the first function corresponding to the first difference instantaneous value ( _X1-2 ); Using the predetermined correspondence information of the second function, identify a second plurality of reasonable values ( _αE , _αF ) of the second function corresponding to the second differential instantaneous value ( _X3-4 ); wherein the second plurality of reasonable values ( _αE , _αF ) are a pair of angle values separated by 180° depending on the angular positions of the first rotor electrode portion (5a) and the second rotor electrode portion (5b), and The angle value closest to the last previously calculated angular position among the second plurality of reasonable values ( _αE , _αF ) is selected as the instantaneous angular position ( _αR ).