JP7737410B2 - Clock oscillator with flexible pivot shaft - Google Patents

Description

The present invention relates to an oscillator with a flexible pivot axis intended to function as a time base in a timepiece mechanism.

An oscillator with a flexible pivot is an oscillator whose balance is guided by an arrangement of elastic parts rather than by a physical rotating shaft sliding in bearings. In addition to guiding rotation, the flexible pivot exerts a return torque on the balance in the same manner as the balance spring in a balance-spring oscillator.

In contrast to oscillators with a balance spring, oscillators with a flexible pivot axis do not generate dry friction during operation, which improves the quality factor.

More specifically, the present invention relates to an oscillator with a flexible pivot axis, the arrangement of elastic elements of which comprises separated cross strips. Such strips extend in different directions in parallel planes so as to cross each other without contact. Oscillators with separated cross strips are described, for example, in European Patent Application No. 2911012, European Patent Application No. 2998800, WO 2016/096677, WO 2017/055983, and WO 2018/109584.

Among known oscillators with separated cross strips, some are intended to be fabricated as a single piece from silicon by DRIE (deep reactive ion etching), while others are formed by assembly of parts. Because multi-level DRIE is complex and expensive to implement and requires the use of specialized techniques to separate the strips, single-piece fabrication is typically preferred when dimensional accuracy is a priority, and assembly fabrication is preferred when ease of manufacture is desired.

As with clock oscillators, the properties of oscillators with separated cross strips are characterized, among other things, by frequency accuracy, quality factor, insensitivity to gravity, insensitivity to temperature, isochronism, and shock resistance.

European Patent Application No. 2911012 European Patent Application No. 2998800 International Publication No. 2016/096677 International Publication No. 2017/055983 International Publication No. 2018/109584

The present invention aims to propose a timepiece oscillator having a separating cross strip that can excel at least some of the above characteristics.

Therefore, the present invention relates to a timepiece oscillator with a flexible pivot axis, comprising a support, a balance, and first and second elastic strips arranged to guide the balance so as to rotate relative to the support about an imaginary axis of rotation and to apply a return torque to the balance, wherein the first and second elastic strips extend in parallel planes and intersect without contacting each other, the balance has a rim that is shaped approximately symmetrically with respect to the imaginary axis of rotation and is assembled between an upper part and a lower part, the upper part comprising an upper section of the support and the first elastic strip, and the lower part comprising a lower section of the support and the second elastic strip.

The applicant has noted that dimensional accuracy of the strips of an oscillator having separate intersecting strips is essential for chronometry. Any deviation of one of the strips from the set dimension will adversely affect chronometry. For this reason, manufacturing of a single piece is preferred, but practical experience has shown that, as recognized in the present invention, manufacturing a flexible pivot shaft having separate intersecting strips by multi-level DRIE is not necessarily, and may even be, less precise than an assembly of overlapping parts, each manufactured by DRIE at a single level and each comprising a strip.

Furthermore, the invention essentially separates the inertia of the oscillator imposed by the balance from the stiffness of the elastic strip, allowing inertia and stiffness to be adjusted separately. The inertia can be easily adjusted in known manner via the attached balance, just as with a standard balance, and the elastic strip can be manufactured with the desired stiffness without dimensional constraints, allowing the correct compromise between stiffness and inertia to be obtained as is typically required for standard oscillators with flexible pivot axes. The materials of the balance and the upper and lower parts can be different and can be optimized according to the function each must fulfill.

Furthermore, the geometric and structural features of the oscillator according to the present invention contribute to improved properties, including insensitivity to gravity, temperature and shock resistance.

Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

1 is a perspective view of a timepiece oscillator according to a particular embodiment of the invention; FIG. FIG. 2 is a perspective view of the same oscillator, but with certain parts removed to simplify the drawing, the oscillator now being shown in relation to a fixed central stop. FIG. 1 is a perspective view showing the balance wheel of this oscillator. FIG. 2 is an axial cross-sectional view of the oscillator.

As shown in Figures 1 to 4, a timepiece oscillator with a flexible pivot shaft according to the present invention for a timepiece, such as a wristwatch, pocket watch, or pendant watch, comprises a support 1, a balance 2, and a flexible pivot shaft 3 connecting the support 1 to the balance 2. The support 1 is intended to be attached to a fixed or movable frame of the timepiece. The flexible pivot shaft 3 comprises first and second elastic strips 4, 5, which are identical but extend in different directions in parallel planes so as to intersect each other without contact. As can be seen in a plan view from above, the point of intersection of the strips 4, 5 coincides with the geometric center of the balance 2. The intersection of the strips 4, 5 defines an imaginary axis of rotation A of the balance 2 relative to the support 1, i.e., an axis of rotation perpendicular to the plane of the oscillator and the plane of the balance 2. The flexible pivot 3 therefore serves to suspend the balance 2 on the support 1, to guide the rotation of the balance 2 relative to the support 1 about an imaginary axis of rotation A, and to exert an elastic return torque on the balance 2 tending to return it to an equilibrium position relative to the support 1 (the position shown in Figures 1 and 2).

In contrast to many oscillators with flexible pivots, the oscillator according to the present invention is not one piece, but is formed by a stack of parts, including an upper part 6, a lower part 7, and a balance 2 between the two. The upper part 6 comprises an upper section 8 of the support 1, a first elastic strip 4, and an upper arm 9 connected to the upper section 8 of the support 1 by the first elastic strip 4. The lower part 7 comprises a lower section 10 of the support 1, a second elastic strip 5, and a lower arm 11 connected to the lower section 10 of the support 1 by the second elastic strip 5.

Each of the upper and lower parts 6, 7 is preferably a one-piece component. The material of these parts 6, 7 is chosen for its good elastic properties and suitability for micromachining. According to a typical embodiment, each of these parts 6, 7 is manufactured from silicon by single-level DRIE, a technique that is relatively simple to implement and allows a high level of precision to be achieved. The silicon parts 6, 7 can be covered with a reinforcing layer, for example a silicon oxide layer, allowing its mechanical strength to be improved. Such a silicon oxide layer can also have a thickness selected to make the oscillator frequency less sensitive to temperature changes (typically 30°C).

The balance 2 comprises a rim 12 and a diametric arm 13, which in the illustrated example is interrupted at its center. The balance 2 can be made at least in part from a dense material such as beryllium, copper, gold, platinum, nickel-silver, or any other dense alloy or metal. The balance can therefore have a small diameter for a given moment of inertia. In this way, friction with the air is reduced, improving the quality factor. The rim 12 of the balance 2 can carry a conventional inertia block 12a, which allows for adjustment of the inertia.

The upper and lower stages 8, 10 of the support 1 are stacked and separated by spacers 14, e.g., metal spacers, and assembled by pins 15. For this purpose, the pins 15 pass through the elastic ends 16 of the upper and lower stages 8, 10 and into holes in the spacers 14. In this way, the stages 8, 10 are fixedly attached to each other only by the elastic clamping of the pins 15. The holes in the spacers 14 through which the pins 15 pass have a diameter slightly larger than that of the pins 15 so as not to bind the elastic strips 4, 5, thereby changing their stiffness and thus the oscillator frequency. The spacers 14 are immobilized relative to the stages 8, 10 by gluing, brazing, or soldering to the pins 15 and/or to at least one of the stages 8, 10.

The upper arm 9, the diametrical arm 13, and the lower arm 11 are superimposed. As with the support 1, a pin 17 passes through the elastic ends 18 of the upper and lower arms 9, 11 and through a hole 19 in the diametrical arm 13. The upper and lower arms 9, 11 are therefore fixedly attached to one another solely by the elastic clamping of the pin 17. The hole 19 in the diametrical arm 13 through which the pin 17 passes has a diameter slightly larger than that of the pin 17 so as not to bind the elastic strips 4, 5. The diametrical arm 13 is immobilized relative to the arms 9, 11 by gluing, brazing, or soldering to the pin 17 and/or at least one of the arms 9, 11. The assembly of the upper arm 9, the balance 2 (by means of its diametrical arm 13), and the lower arm 11 forms a rigid oscillating unit.

Assembling the balance 2 with the upper and lower parts 6 and 7 using arms 9, 11, and 13 ensures the oscillator has good mechanical strength and high assembly precision. Furthermore, if an impact causes the balance 2 to rotate excessively, and regardless of the direction of rotation of the balance 2, the diametric arm 13 abuts against the support 1, or more precisely, against the spacer 14, protecting the elastic strips 4 and 5 before the elastic limit of these strips is exceeded.

Each of the resilient ends 16, 18 of the upper and lower stages 8, 10 and the upper and lower arms 9, 11 can be formed by a resilient arm, preferably three resilient arms, that clamps the corresponding pins 15, 17. Contact between each resilient arm and the pins 15, 17 can be point contact, as shown, to ensure contact between the resilient ends 16, 18 and the pins 15, 17 only at discrete points. This allows for extremely accurate alignment of the upper and lower components 6, 7.

Apart from the benefits in terms of manufacturing precision, the assembly of the upper and lower parts 6, 7 with the balance 2 allows for true physical separation of the elastic strips 4, 5, which is easier to achieve than with one-piece manufacturing.

The assembly of arms 9, 11, and 13 suspends balance 2 on support 1 via elastic strips 4 and 5, with diametric arm 13 acting as a spacer for upper and lower arms 9 and 11. Balance 2 constitutes the inertial portion of the oscillator, while the inertia of upper and lower arms 9 and 11 can be ignored. By attaching the balance to the flexible pivot shaft rather than as an integral part, the present invention decouples the inertial portion of the oscillator from the rigidity of the flexible pivot shaft, facilitating adjustment of the oscillator frequency. Meanwhile, the inertia and imbalance of balance 2 and the torque of flexible pivot shaft 3 can be easily measured and compensated for independently of each other. Furthermore, it is possible to pair balance 2 with flexible pivot shaft 3, i.e., to obtain a desired frequency, it is possible to associate a balance with a selected moment of inertia with a flexible pivot shaft that generates a selected torque.

According to another advantageous feature of the present invention, the oscillator according to the present invention comprises an upper abutment member 20 and a lower abutment member 21 attached to the upper surface of the upper part 6 and the lower surface of the lower part 7, respectively. These abutment members 20, 21 are assembled by a pin 22 passing through the arms 9, 11, 13. The central stud 23 of the upper abutment member 20, which is centered on the imaginary axis of rotation A, is engaged with clearance in a bore 24 of an upper stop 25, which is fixed relative to the support 1. Similarly, the central stud 26 of the lower abutment member 21, which is centered on the imaginary axis of rotation A, is engaged with clearance in a bore 27 of a lower stop 28, which is fixed relative to the support 1.

During normal operation of the oscillator, the studs 23, 26 rotate within the bores 24, 27 without touching their walls. The studs 23, 26 do not constitute pivots guided in bearings, but simple movable stops that can contact the fixed stops 25, 28 if the watch is subjected to a shock. In the event of a radial shock, the studs 23, 26 can abut against the side walls of the bores 24, 27. In the event of an axial shock, one of the studs 23, 26 can come to rest against the bottom of the bore 24, 27, or more generally, one of the abutment members 20, 21 can come to rest against the corresponding fixed stop 25, 28. The cooperation between the abutment members 20, 21 and the fixed stops 25, 28 protects the elastic strips 4, 5 by preventing them from deforming beyond their elastic limit in the event of a radial or axial shock.

The upper abutment member 20 and the lower abutment member 21 are typically made from a metal material that may be the same as or different from that of the balance 2. The pin 22 can be driven into the abutment members 20, 21 and the diametric arm 13 of the balance 2, and can pass through the upper and lower arms 9, 11 with clearance.

The stud-bore arrangement can be reversed, in other words, the fixed stops 25, 28 can comprise studs and the abutment members 20, 21 can comprise bores.

The arrangement of the balance 2 between the upper and lower parts 6, 7 allows the balance 2, and more generally the entire rigid oscillating unit 2, 9, 11, 20, 21, to have a center of mass that is substantially located in the mid-plane of the flexible pivot axis 3 between the parallel planes in which the elastic strips 4, 5 extend, respectively. This reduces the risk of the balance 2 tilting during the wearer's arm movements, in the event of a shock, or under the influence of gravity. Tilting could disrupt the time measurement by deforming the elastic strips 4, 5 from their plane of motion, or even cause the abutments 20, 21 to rub against the fixed stops 25, 28. Furthermore, the arrangement of the balance 2 between the upper and lower parts 6, 7 makes the oscillator frequency less sensitive to temperature. In the event of thermal expansion of the oscillator, the metal balance 2 deforms differently than the silicon arms 9, 11. The arrangement according to the invention makes it possible to avoid the upper and lower parts 6, 7 (made of silicon) bending and torsionally deforming the strips 4, 5 and thus modifying their stiffness.

Since the balance 2 and its rim 12 have a general shape symmetrical with respect to the imaginary axis of rotation A, thermal expansion of the balance 2 does not or only slightly alters the position of its centre of gravity, thus avoiding increased deviations in operation between different positions of the watch at the nominal operating amplitude. Furthermore, the rim 12 is preferably annular so as to optimise the ratio of inertia to mass of the balance 2 and, consequently, reduce the frequency sensitivity of the oscillator to its orientation relative to gravity.

According to a further advantageous feature of the present invention, which can be seen in FIG. 1, an imbalance adjustment element 29 is attached to the balance 2. This imbalance adjustment element 29 is attached to the upper abutment member 20 at the center of the balance 2 in order to modify the balance 2's inertia as little as possible. This imbalance adjustment element 29 is elastically held by the central stud 23 of the upper abutment member 20, which passes through a slot 30 in the element 29, thereby elastically deforming the slot 30. The slot 30, in a plan view from above, is oriented along the axis of symmetry of the flexible pivot shaft 3, which passes between the points where the flexible pivot shaft 3 joins with the support 1. A peg 31 driven into the upper abutment member 20 and passing through the slot 30 guides the imbalance adjustment element 29 to translate along the axis of symmetry when the element 29 is displaced by the watchmaker to adjust the imbalance of the balance 2.

In accordance with the teachings of International Patent Application No. PCT/IB2020/056370 (the contents of which are incorporated by reference), the imbalance adjustment part 29 allows the center of mass of the balance 2, or more precisely the center of mass of the entire rigid oscillating unit to which the balance 2 belongs, to be positioned on the axis of symmetry of the flexible pivot axis 3 at a position different from the position of the imaginary axis of rotation A, said position being selected to minimize the dependence of the oscillation frequency on the direction of gravity for a given oscillation amplitude. The adjustment inertia block 12a carried by the balance 2 can be used to compensate for the correction of the inertia of the balance 2 caused by the imbalance adjustment.

The balance 2 may carry a portion 33 or have a protrusion or recess that allows a certain imbalance to be achieved immediately after manufacture, and the imbalance adjustment part 29 thus functions as a fine adjustment element. As shown in Figures 1 and 3, the portion 33 may be in the form of an arc of a circle centered on the imaginary axis of rotation A and may be pierced by an aperture 34, the function of which is to allow optical measurement (by means of a laser diode) of the amplitude of the balance 2 as a function of time.

To cooperate with the escapement fork, the oscillator according to the invention can be provided with a conventional pin 35. This pin 35 can be held by the lower abutment 21, as shown. Alternatively, it can be held by the upper abutment 20 or by the upper and lower arms 9, 11.

It should be noted that the assembly method of the balance 2 and the upper and lower parts 6, 7 by the pin 17 is independent of the shape of the balance 2 and its rim 12 and the order in which the parts 2, 6, 7 are stacked.

Claims (14)

A timepiece oscillator with a flexible pivot axis, comprising a support (1), a balance (2), and first and second elastic strips (4, 5) arranged to guide the balance (2) so that it rotates relative to the support (1) about an imaginary axis of rotation (A) and to apply a return torque to the balance (2),
a timepiece oscillator, wherein the first and second elastic strips (4, 5) extend in parallel planes and cross each other without contacting each other, the balance (2) constitutes the inertial part of the timepiece oscillator, the balance (2) having a rim (12) that is shaped approximately symmetrically with respect to the imaginary axis of rotation (A) and being assembled between an upper part (6) and a lower part (7), the upper part (6) comprising an upper section (8) of the support (1) and the first elastic strip (4), and the lower part (7) comprising a lower section (10) of the support (1) and the second elastic strip (5). a diametric arm (13) forming part of said balance (2), an upper arm (9) forming part of said upper part (6), and a lower arm (11) forming part of said lower part (7),
the balance (2) is assembled to the upper and lower parts (6, 7) by superimposing and assembling the three arms (9, 11, 13),
2. A timepiece oscillator according to claim 1. the assembly of the three arms (9, 11, 13) is capable of abutting against the support (1) in each of the two rotational directions of the balance (2) before the elastic limit of the first and second elastic strips (4, 5) is exceeded in the event of excessive rotation of the balance (2);
3. A timepiece oscillator according to claim 2. the three arms (9, 11, 13) are assembled by a pin (17) that is resiliently clamped by the resilient portions (18) of the upper and lower arms (9, 11) and passes with clearance through the diametric arm (13);
the diametrical arm (13) is fixed to the upper and lower arms (9, 11) by gluing, brazing or soldering;
4. A timepiece oscillator according to claim 2 or 3. the balance (2) is assembled to the upper and lower parts (6, 7) by means of a pin (17) which is resiliently clamped by the elastic parts (18) of the upper and lower parts (6, 7) and passes through the balance (2) with a clearance,
the balance (2) is fixed to the upper and lower parts (6, 7) by gluing, brazing or soldering;
4. A timepiece oscillator according to claim 1, wherein the timepiece oscillator comprises: A timepiece oscillator as claimed in claim 4 or 5, characterized in that the elastic part (18) is in contact with the pin (17) only at discrete points. A timepiece oscillator as claimed in any one of claims 1 to 6, characterized in that each of the upper and lower parts (6, 7) is an integral part. A timepiece oscillator according to any one of the preceding claims, characterized in that the balance (2) is made from a material different from that of the upper and lower parts (6, 7). A timepiece oscillator according to claim 8, characterized in that the balance (2) is made from a material denser than the material of the upper and lower parts (6, 7). 10. A timepiece oscillator according to any one of the preceding claims, characterized in that the balance (2) is made of metal or alloy. A timepiece oscillator according to any one of the preceding claims, characterized in that the upper and lower parts (6, 7) are made from a silicon-based material. A timepiece oscillator according to any one of the preceding claims, characterized in that the rim (12) is annular. It has upper and lower abutment members (20, 21) at the center,
said upper and lower abutment members (20, 21) are fixedly attached to said balance (2) and are capable of abutting, in the event of an impact, against stops (25, 28) fixed relative to said support (1) before the elastic limit of said first and second elastic strips (4, 5) is exceeded;
13. A timepiece oscillator according to any one of claims 1 to 12 . an imbalance adjusting element (29) attached to the balance (2);
the imbalance adjustment component (29) is arranged to be guided in translation along an axis of symmetry of the first and second elastic strips (4, 5), which passes between the points at which the first and second elastic strips (4, 5) join to the support (1) when viewed in a plan view from above;
14. A timepiece oscillator according to any one of claims 1 to 13 .