HK1240335B - Timepiece comprising a wheel set with a determinable angular position - Google Patents

Description

Timepiece comprising a wheel set having a determinable angular position

Technical Field

The invention relates to the technical field of timepieces comprising a timepiece movement provided with an analog display mechanism and at least one wheel set rotating integrally with a rotation indicator of the analog display mechanism.

Background Art

To determine the angular position of such a wheelset, EP Patent 0952426 discloses providing the wheelset with a surface layer made of a special material and a through-hole located in an intermediate region between the wheelset's axis of rotation and its outer circumference. When the wheelset is in a reference position, a proximity sensor, stationary relative to the wheelset, is positioned directly above or below the hole. This sensor is capable of sensing the special material and provides a measurement signal that varies depending on the proximity of the material. Consequently, when the hole passes over the sensor, the measurement signal exhibits a specific shape, such as a spike.

To determine the angular position of the wheelset, it is proposed to use a stepper motor to make the wheelset complete one step-by-step rotation while simultaneously recording the measurement signal. The aforementioned peaks thus indicate that the wheelset has passed through its reference position. Once the reference position has been determined in the graph representing the measurement signal, it is easy to deduce from it the angular position of the wheelset corresponding to another point on the graph, in particular its initial angular position, i.e., its position before it begins to rotate.

EP Patent 0952426 proposes the use of inductive or capacitive sensors, but notes that capacitive sensors are more sensitive than inductive sensors to environmental disturbances and to interference caused by manufacturing and assembly tolerances. Capacitive sensors are particularly affected by the axial play between the wheelset and the sensor along the wheelset's axis of rotation. The greater this axial play, the wider the peak: the accuracy of the angular reference position determination is therefore directly affected by the axial play.

Summary of the Invention

One object of the present invention is to overcome the above-mentioned drawbacks by proposing a solution for determining the angular position of a wheelset by means of a capacitive sensor whose accuracy is not affected by variations in the axial play between the wheelset and the sensor.

To this end, the present invention relates to a timepiece comprising:

a timepiece movement provided with an analog display mechanism and at least one wheel set rotating integrally with a rotation indicator of said analog display mechanism, said wheel set comprising a conductive plate extending substantially orthogonally to the axis of rotation of said wheel set and pierced by at least one hole,

- detection means for detecting the reference angular position of the aperture, the detection means comprising at least one set of planar electrodes comprising a first electrode, a second electrode and a common electrode arranged in a plane parallel to the wheel set, the common electrode being arranged along a portion of the first electrode and a portion of the second electrode,

The hole at least partially:

- above or below said first electrode at a position referred to as a first imbalance position,

- above or below said first electrode and said second electrode at a position called equilibrium position,

- above or below said second electrode at a position referred to as the second imbalance position.

The first electrode and the common electrode form a first capacitor having a capacitance C1, and the second electrode and the common electrode form a second capacitor having a capacitance C2. Using a stepper motor that causes the wheel set to complete one full step rotation and a measurement circuit that generates a measurement signal representing the number of steps as a function of the number of steps, a curve with maximum and minimum values is obtained. The minimum value is observed when the hole is in the first unbalanced position; the maximum value is observed when the hole is in the second unbalanced position; and the curve has a zero value when the hole is in the balanced position.

Since maxima and minima are characteristic of specific angular positions of the wheel set, once a maximum or minimum has been identified on a graph representing the measurement signal, it is possible to infer the angular position of the wheel set corresponding to another point on the graph. In particular, it is possible to infer the initial angular position of the wheel set, i.e. its position before it started to rotate, which is the position to be sought.

The use of differential capacitance measurement, rather than a single capacitance measurement as in the prior art, allows the shape of the curve to be independent of the axial play between the wheelset and the electrode. Consequently, even when the axial play is large, the maximum and minimum values on the curve can be accurately identified. Furthermore, identifying two characteristic positions of the wheelset on the curve, rather than a single position as in the prior art, makes the determination of the wheelset's angular position more reliable.

Additionally, it should be noted that a "planar electrode" refers to a conductive portion that extends substantially in at least two directions on one plane, as opposed to a rod-shaped electrode.

In addition, the wheel set plate may include a plurality of holes and the detection device may include a plurality of groups of electrodes of the above type. In this case, at a specific position of the wheel set, each hole is arranged to be opposite to the first and second electrodes of a group of electrodes.

Furthermore, the timepiece may comprise one or more of the following features in any technically possible combination.

In one non-limiting embodiment, all three electrodes have substantially the same area. This configuration results in a significant disequilibrium between capacitance C1 and capacitance C2, and thus a large absolute value of the amplitude of the maximum and minimum values of the curve. In addition, it should be noted that in some configurations of the electrodes, the curve has a step between the peak corresponding to the maximum value and the valley corresponding to the minimum value. A step means a section with a reduced slope on both sides of the section. The configuration just described can minimize the length of this step.

In one non-limiting embodiment, in the first unbalanced position, the balanced position and the second unbalanced position, the hole is at least partially located above or below the common electrode. This configuration allows particularly sharp peaks and valleys to be obtained.

In one non-limiting embodiment, in the equilibrium position, all three electrodes are located above or below the hole. The hole in the wheel set can therefore be smaller than all the electrodes. This configuration makes it possible to eliminate any steps between the peaks and valleys of the curve.

In one non-limiting embodiment, the common electrode comprises two planar half-electrodes electrically connected to each other, the half-electrodes being arranged on either side of the assembly formed by the first and second electrodes.

In one non-limiting embodiment, the common electrode comprises two planar half-electrodes electrically connected to each other, the two half-electrodes being arranged between the first and second electrodes.

In one non-limiting embodiment, the first and second electrodes are arranged side by side, with the common electrode extending substantially along the shape of an annular portion of the first and second electrodes. This configuration allows the use of first and second electrodes having very large surface areas, for example, first and second electrodes whose combined surface area is substantially the surface area of the aperture. The large surface areas of the first and second electrodes result in large absolute values for the amplitudes of the maxima and minima on the curve.

The invention also relates to a method for determining the angular position of a wheel set of a timepiece movement as described above, comprising:

- for example, by using a stepper motor to rotate the wheel set in steps,

- simultaneously with the rotation, measuring as a function of the number of rotation steps, wherein C1 is the capacitance of the capacitor formed by the first electrode and the common electrode, C2 is the capacitance of the capacitor formed by the second electrode and the common electrode,

- detecting the maximum and minimum values on the curve representing the measurement results,

The angular position of the wheelset is determined using the detected maxima and minima.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will become apparent from the following description given by way of non-limiting illustration with reference to the accompanying drawings, in which:

1 shows a detection device for detecting the angular position of a rotating wheel set of a timepiece movement, superimposed above said wheel set, in a first embodiment of the invention.

- Figure 2a shows the detection device of Figure 1 with the rotating wheel set in a first angular position that it occupies during one complete rotation of said wheel set starting from an initial angular position.

FIG. 2 b shows a measurement curve obtained stepwise during a rotation of the wheelset in a state corresponding to the position of the wheelset in FIG. 2 a .

FIG. 3 a shows the detection device of FIG. 1 , with the rotating wheel set in a second angular position, called the first imbalance position, that it occupies during one complete rotation of said wheel set starting from the initial angular position.

FIG. 3 b shows the measurement curve in a state corresponding to the position of the wheel set in FIG. 3 a .

FIG. 4 a shows the detection device of FIG. 1 , with the rotating wheel set in a third angular position, called the equilibrium position, that it occupies during one complete rotation of said wheel set starting from the initial angular position.

FIG. 4 b shows the measurement curve in a state corresponding to the position of the wheel set in FIG. 4 a .

FIG. 5 a shows the detection device of FIG. 1 , with the rotating wheel set in a fourth angular position, called the second imbalance position, that it occupies during one complete rotation of said wheel set starting from the initial angular position.

FIG. 5 b shows the measurement curve in a state corresponding to the position of the wheel set in FIG. 5 a .

- Figure 6a shows the detection device of Figure 1 with the rotating wheel set in a fifth angular position occupied during one complete rotation of said wheel set starting from the initial angular position.

- FIG. 6 b shows the measurement curve in a state corresponding to the position of the wheel set in FIG. 6 a .

- Figure 7a shows the detection device of Figure 1 , with the rotating wheel set returning to its initial angular position after said wheel set has completed one complete rotation.

- FIG. 7 b shows the measurement curve in a state corresponding to the position of the wheel set in FIG. 7 a .

- Figure 8 shows one such device according to a second embodiment of the invention.

- Figure 9 shows one such device according to a third embodiment of the invention.

- Figure 10 shows such a device according to a fourth embodiment of the invention.

- Figure 11 shows one such device according to a fifth embodiment of the invention.

DETAILED DESCRIPTION

The present invention relates to a timepiece comprising a timepiece movement. The timepiece movement comprises a wheel set MB in the form of a disc, which also comprises an arbour defining a geometric axis of rotation. The timepiece movement is associated with an analog display mechanism comprising a rotating indicator (not shown) fixedly mounted on the arbour. This indicator can be used to indicate the hours, minutes, seconds, or any other information suitable for an analog display.

Wheelset MB includes a conductive plate PT extending substantially perpendicular to the axis of rotation of wheelset MB. This plate PT is pierced with a through-hole OV in the form of an annular portion, arranged in an area intermediate between the outer periphery of the plate PT and a central hole provided for passage of a spindle. This through-hole OV extends, for example, over 120 degrees.

Opposite the wheel set MB, above or below it, a plate PA is positioned, for example in the form of a semi-circular disk. Plate PA extends substantially parallel to the plate PT of the wheel set MB and perpendicular to the axis of rotation of the wheel set MB. Advantageously, plate PA is a printed circuit board (PCB) on which three planar electrodes are printed. Unlike the wheel set, plate PA is fixed: the wheel set can therefore rotate relative to plate PA.

Plate PA includes a set of electrodes. This set of electrodes comprises three planar electrodes, designated as a first electrode E1, a second electrode E2, and a common electrode Em. The three electrodes E1, E2, and Em are in the form of annular segments. The common electrode Em is arranged along a portion of the first electrode E1 and a portion of the second electrode E2, so as to form a first capacitor with capacitance C1 with the first electrode E1 and a second capacitor with capacitance C2 with the second electrode E2. Due to the presence of the aperture OV in plate PT, the capacitances C1 and C2 depend on the angular position of the wheel set MB relative to the electrodes E1, E2, and Em. In particular, when the aperture OV is located above the first electrode E1 and the common electrode Em, or respectively above the second electrode E2 and the common electrode Em, the capacitance C1, or respectively C2, is maximum, because the transfer of charge from one electrode to the other is no longer facilitated by the presence of the conductive material of plate PT.

FIG1 shows a first configuration of these electrodes E1, E2, Em on plate PA. In this configuration, the three electrodes E1, E2, Em have substantially the same surface area, with the common electrode Em positioned between the first and second electrodes E1, E2. Furthermore, the total surface area of the electrodes E1, E2, Em is substantially the same as the surface area of the aperture OV. In the embodiment shown in FIG1 , the aperture OV extends over 120 degrees, and each electrode extends over 120/3*0.98=38 degrees (these angular characteristics are, of course, not limiting). Consequently, there exists an angular position of the wheel set MB relative to plate PA (shown in FIG4 a ) in which the three electrodes are completely opposite the aperture OV, and the aperture OV is completely opposite the electrodes E1, E2, Em.

To determine the initial angular position of wheelset MB (which, in the non-limiting example presented below, is the angular position of FIG. 1 ), it is proposed to cause wheelset MB to complete one complete step-by-step rotation about its axis of rotation. This rotation is achieved by a stepper motor (not shown). The stepper motor is, for example, a bipolar Lavet-type motor. The transmission from the motor to the wheelset (not shown) is preferably formed by a reduction gear train. An electronic measuring circuit, for example comprising a microcontroller, is arranged to measure the value of as a function of the number of steps applied to wheelset MB and to generate a measurement curve CB.

Figures 2a, 3a, 4a, 5a, 6a, and 7a illustrate the successive angular positions of the wheel set MB relative to the plate PA during one complete rotation of the wheel set MB, starting from the position of Figure 1. In the position of Figure 2a, only the first electrode E1 is opposite the hole OV of the wheel set MB. In the position of Figure 3a, the first electrode E1 and the common electrode Em are positioned opposite the hole OV. In the position of Figure 4a, all three electrodes E1, E2, and Em are opposite the hole. In the position of Figure 5a, the common electrode Em and the second electrode E2 are opposite the hole. In the position of Figure 6a, only the second electrode E2 is opposite the hole OV. Finally, in the position of Figure 7a, the wheel set MB has returned to its initial position, with none of the three electrodes E1, E2, and Em opposite the hole OV.

2b, 3b, 4b, 5b, 6b and 7b show measurement curves CB as a function of the number of steps N applied to wheel set MB at moments corresponding to the positions occupied by wheel set MB in FIGS. 2a, 3a, 4a, 5a, 6a and 7a.

As shown in Figure 2b, from the initial position of wheel set MB to the position shown in Figure 2a, the measurement curve CB has a zero value. Then, as shown in Figure 3b, the value of decreases between the positions shown in Figure 2a and 3a. Curve CB reaches a minimum when, and only when, both electrode E1 and common electrode Em are opposite aperture OV.

As shown in FIG4b, between the positions of FIG3a and FIG4a, the values of curve CB increase until they return to zero. Then, as shown in FIG5b, between the positions of FIG4a and FIG5a, the values of increase. Curve CB reaches its maximum value when and only when both electrode E2 and common electrode Em are opposite aperture OV.

Then, as shown in Figure 6b, between the position of Figure 5a and the position of Figure 6a, the value of curve CB decreases and returns to zero. Finally, until wheel set MB returns to its initial angular position, curve CB has a value of zero.

Curve CB is then used to calculate two characteristic positions of wheel set MB. At the first characteristic position, corresponding to the position in Figure 3a , curve CB has a minimum; at the second characteristic position, corresponding to the position in Figure 5a , curve CB has a maximum. Since the number of steps required to reach the positions corresponding to the minimum and maximum can be determined from curve CB, the initial position of wheel set MB can be easily deduced from it.

Different configurations of the electrodes E1 , E2 , Em on the plate PA and/or of the holes OV on the plate PT than those proposed with reference to FIG. 1 are possible.

In the configuration of FIG8 , the electrodes E1, E2, Em are similar to those of FIG1 , but the aperture OV extends only over 80 degrees (naturally, this angular aperture is not restrictive). Consequently, there is no angular position of the wheelset MB in which all three electrodes are opposite the aperture OV. This configuration avoids the steps observed in FIG7 b between the peaks corresponding to the maxima and the valleys corresponding to the minima.

In the configuration of FIG9 , the three electrodes E1, E2, and Em do not have the same surface area: the first electrode E1 and the second electrode E2 have the same surface area, but the common electrode Em has a larger surface area. In the embodiment shown in FIG9 , the first electrode E1 and the second electrode E2 extend over 10 degrees, while the common electrode Em extends over 18 degrees (naturally, these angular characteristics are not limiting). However, the aperture OV extends over 120 degrees: the surface area of the aperture OV is therefore much larger than the sum of the surface areas of the electrodes E1, E2, and Em.

In the configuration of FIG10 , the first electrode E1 and the second electrode E2 are arranged side by side, and the common electrode Em is formed by two electrically connected half-electrodes (the connection is not shown). The half-electrodes are arranged on both sides of the assembly formed by the first electrode E1 and the second electrode E2. It should be noted that, alternatively, the two half-electrodes can be arranged between the first electrode E1 and the second electrode E2.

In the configuration of FIG11 , the first electrode E1 and the second electrode E2 are arranged side by side, with the common electrode Em positioned along the outer portions of the electrodes E1 and E2. Furthermore, the combined surface area of the first and second electrodes E1 and E2 is substantially equal to the surface area of the aperture OV. Therefore, there is no angular position where the common electrode Em is opposite the aperture OV. This configuration increases the surface area of the first and second electrodes E1 and E2, thereby increasing the amplitude of the peaks and valleys of the measurement curve CB. Furthermore, this configuration avoids the steps observed in FIG7b between the peaks corresponding to the maximum values and the valleys corresponding to the minimum values.

Of course, the invention is not limited to the examples shown, but is capable of various variations and modifications readily apparent to those skilled in the art. For example, the wheel set MB could be pierced with K holes OV, K ≥ 2, and the plate PA could include K sets of three electrodes, similar to those described above. This would allow for greater absolute peak and valley amplitudes in the measurement curve.

Claims (8)

1. A clock, comprising: - A watch movement comprising an analog display mechanism and at least one wheel assembly (MB) integrally rotating with a rotation indicator of the analog display mechanism. The wheel assembly (MB) includes a conductive plate (PT) extending substantially orthogonal to the rotation axis of the wheel assembly (MB) and having at least one through-hole (OV). - A detection device for detecting the reference angular position of the hole (OV), the detection device comprising at least one set of planar electrodes, the planar electrodes comprising a first electrode (E1), a second electrode (E2), and a common electrode (Em) arranged in a plane parallel to the wheel assembly (MB), the common electrode (Em) being arranged along a portion of the first electrode (E1) and a portion of the second electrode (E2). - An electronic measurement circuit configured to measure the value of C1 as a function of the number of steps applied to the wheel assembly (MB), wherein C1 is the capacitance of a capacitor formed by the first electrode (E1) and the common electrode (Em), and C2 is the capacitance of a capacitor formed by the second electrode (E2) and the common electrode (Em). The orifice (OV) is at least partially: -The location referred to as the first imbalance position is located above or below the first electrode (E1). - The position, referred to as the equilibrium position, is located above or below the first electrode (E1) and the second electrode (E2). - The location, known as the second imbalance position, is located above or below the second electrode (E2). 2. The clock according to claim 1, characterized in that all three electrodes (E1, E2, Em) have substantially the same area. 3. The clock according to claim 2, wherein, in the first unbalanced position, the balanced position and the second unbalanced position, the hole (OV) is at least partially located above or below the common electrode (Em). 4. The clock according to claim 3, characterized in that, in the balanced position, the three electrodes (E1, E2, Em) are completely located above or below the hole (OV). 5. The clock according to claim 1, wherein the common electrode (Em) comprises two planar half-electrodes (Em1, Em2) electrically connected to each other, the half-electrodes (Em1, Em2) being arranged on both sides of the assembly formed by the first electrode (E1) and the second electrode (E2). 6. The clock according to claim 1, wherein the common electrode (Em) comprises two planar half-electrodes (Em1, Em2) electrically connected to each other, the half-electrodes (Em1, Em2) being arranged between the first electrode (E1) and the second electrode (E2). 7. The clock according to claim 1, characterized in that the first electrode (E1) and the second electrode (E2) are arranged side by side, and the common electrode (Em) extends substantially in the shape of an annular portion along the first electrode (E1) and the second electrode (E2). 8. A method for determining the angular position of the wheel assembly (MB) of the watch movement according to claim 1, comprising: - To cause the wheel assembly (MB) to rotate in a stepwise manner, Simultaneously with the rotation, a value is measured as a function of the number of rotation steps, where C1 is the capacitance of the capacitor formed by the first electrode (E1) and the common electrode (Em), and C2 is the capacitance of the capacitor formed by the second electrode (E2) and the common electrode (Em). -Detect the maximum and minimum values on the curve (CB) representing the measurement results. - The angular position of the wheel assembly (MB) is determined by using the detected maximum and minimum values.