EP4246245A1

EP4246245A1 - Movement for a watch

Info

Publication number: EP4246245A1
Application number: EP22163102.1A
Authority: EP
Inventors: Maarten Pieter LUSTIG; Eola Jessica Giuffre; Aleksandar JOVIC; Roemer Michiel HELWIG; Joep MEIJ
Original assignee: Flexous Mechanisms Ip BV
Current assignee: Flexous Mechanisms Ip BV
Priority date: 2022-03-18
Filing date: 2022-03-18
Publication date: 2023-09-20
Also published as: WO2023175194A1

Abstract

The invention relates to a movement for a watch, which movement comprises an escape wheel (9) having a plurality of teeth (10) and an oscillator (1) having anchor teeth (8), which anchor teeth (8) are controlled by the oscillator (1) to alternately block and release the teeth (10) of the escape wheel (9), wherein at least the escape wheel and the anchor teeth (10, 8) share an imaginary plane (P). At least some of the teeth (10) of the escape wheel (9) and/or at least one of the anchor teeth (8) of the oscillator (1) comprises two surfaces defining a circumferential edge (10B, 8B) that is aligned with the end surfaces (8A, 10A) of the teeth (8, 10) of the other.

Description

The invention relates to a movement for a watch, which movement comprises an escape wheel having a plurality of teeth and an oscillator having anchor teeth, typically a so-called entry pallet or tooth and an exit pallet or tooth, which anchor teeth are controlled by the oscillator, e.g. are an integral part of or attached to the oscillator, to alternately block and release the teeth of the escape wheel, wherein at least the escape wheel and the anchor teeth, preferably the entire oscillator, share an imaginary plane, i.e. are planar.
NL 2024076 relates to a mechanical watch comprising an oscillator embodied with a vibratory mass or masses, wherein each vibratory mass connects to least one flexural member. The watch further comprises an escape wheel and anchor teeth that are connected to the vibratory mass or masses, which anchor teeth cooperate with the escape wheel, and wherein the anchor teeth are provided on at least one of the flexural members.
WO 2018/100122 relates to a device for a timepiece, comprising a base, an inertial regulating organ mounted to rotate relative to the base, by means of an elastic suspension means connecting the regulating organ to the base. The device comprises an anchor adapted to engage with an energy distribution member (escape wheel) provided with teeth and intended to be urged by an energy storage device, said anchor being controlled by said regulating member to regularly and alternately block and release the energy distribution member.
It is an object of the present invention to improve consistency of energy transfer between the oscillator and the escapement wheel and/or improve stability of the oscillator frequency, and thus provide more accurate time keeping.
To this end, at least some, preferably most or each of the teeth of the escape wheel and/or at least one, preferably each of the anchor teeth of the oscillator comprises two surfaces defining a circumferential edge, i.e. an edge extending along and/or defining part of the circumference of the escape wheel or anchor teeth, seen in top view, that is aligned with the end surfaces of the teeth of the other.
In an embodiment, the end surfaces of the teeth of the escape wheel and/or of the anchor teeth define circumferential edges, preferably sharp edges, i.e. edges that, seen in cross-sectional side view, have an angle smaller than 90°, with the upper or lower surface of the escape wheel teeth and/or anchor teeth.
E.g. the escape wheel has a flat top surface, and typically a flat bottom surface parallel to the top surface, and the end surfaces of the teeth of the escape wheel are (slightly) oblique defining, seen in cross-section, a sharp edge with the top surface or the bottom surface of the escape wheel. Similarly, the oscillator including the anchor teeth has a flat top surface, and typically a flat bottom surface parallel to the top surface, and the end surfaces of the anchor teeth define a sharp edge with the top surface of the anchor teeth or oscillator. By aligning the edges of the escape wheel teeth with the end surfaces of the anchor teeth, or vice versa, impact between the two, in particular during impulse, i.e. during transfer of energy from the escape wheel to the oscillator, is more consistent and as a result the frequency of the oscillator is more stable, ultimately resulting in more accurate time keeping.
The edges may have an angle smaller than 89,5°, preferably smaller than 89°, preferably smaller than 88°. In principle, even sharper edges are preferred, although angles smaller than 80° are more time consuming to produce, i.e. angles in a range from 80° to 89,5° are preferred.
Consistency can be further improved if the escape wheel and anchor teeth are configured such that during impulse and at the point of contact or line of contact the angle between the end surface(s) of the escape wheel tooth and the end surface(s) of the anchor tooth is larger 1°, preferably larger than 3°, preferably larger than 5°, preferably larger than 10°. It was found that at such angles electrostatic forces between the end surfaces of the teeth of the escape wheel and the anchor teeth are reduced significantly.
In an embodiment, the circumferential edges on the teeth of the escape wheel are, at least when the edge is in contact with an end surface, located between the upper and lower surfaces of the anchor teeth or vice versa, i.e., the circumferential edges on the anchor teeth are located between the upper and lower surfaces of the teeth of the escape wheel.
In a refinement, the circumferential edges on the teeth of the escape wheel are, at least when the edge is in contact with an end surface, located at least 50 µm, preferably at least 75 µm, preferably at least 100 µm removed from the upper and lower surfaces of the anchor teeth or vice versa.
The escape wheel, the oscillator and/or the anchor teeth may have a thickness smaller than 700 µm, preferably smaller than 550 µm, e.g. in a range from 250 µm to 500 µm.
It is preferred that the oscillator and the anchor teeth are monolithic, i.e. made from a single piece.
A very efficient way of providing oblique end surfaces is by shaping the escape wheel, the oscillator and/or the anchor teeth by means of reactive ion edging, such as RIE or DRIE and preferably from silicon.
The advantages of the present invention are particularly pronounced in so-called dead beat escapements, in escapements wherein the amplitude of the anchor teeth is at least substantially equal to the amplitude of the oscillator, and/or in escapements with low torque escape wheels, such as escape wheels having a torque of less than 300 nanoNewtonmeter, less than 200 nNm or even less than 150 nNm. Torque is typically generated by a main spring and transmitted via a gear train.
The oscillator may have an amplitude smaller than 30°, preferably smaller than 20°, preferably smaller than 15°, e.g. in range from 3° to 10°. In this context, amplitude refers to the degrees of rotation of the oscillator from its neutral (or central) position to one of its extreme positions, in clockwise (CW) or counterclockwise (CCW) direction, with the main spring fully wound and the movement in a horizontal and stationary position.
The oscillator may have a natural frequency of 15 Hertz (Hz) or higher, preferably 25 Hz or higher, preferably 35 Hz or higher. In extreme instances, natural frequencies could be up to 100 Hz or even higher.
The invention further relates to a movement comprising a base, e.g. a base plate or platine, and the oscillator comprises a ground that is mounted to the base and an oscillatory mass that is suspended to the ground via one or more elastic links, typically a plurality of links, e.g. two or four links, and/or an escape wheel that is rotatably mounted to or in the base. In an embodiment, the ground, the one or more elastic links, and the mass form a compliant mechanism and/or are monolithic, i.e. made from one piece.
In an example, the escape wheel comprises a central shaft rotatably mounted in a bearing, such as rubies, on or in the base plate and on or in a bridge extending over the escape wheel. The movement may comprise an energy storage, typically a mainspring, in particular a spiral spring in a geared barrel, a gear train, e.g. comprising a center wheel, a third wheel (carrying or coupled to the minute and hour hands of the watch), and a fourth wheel (carrying or coupled to the second hand) of the watch, to transmit torque and energy to the escape wheel. The invention also relates to a wrist watch comprising such a movement.
The invention also relates to a wristwatch comprising a movement as described above.
WO 2019/156552 relates to a mechanical watch oscillator comprising a platform and at least two vibratory masses that are individually suspended on the platform with at least one flexural member. When the masses are vibrating, extensions (reference signs 51, 52 in the drawings of WO 2019/156552 ) of these masses alternatively release and block an escape wheel, allowing the escape wheel to rotate in steps.
Below, the invention will be explained further, which reference to the appended figures in which an embodiment of the invention is shown.

Figures 1 and 2 are a perspective view and a top plan view of an oscillator and escape wheel according to the present invention.
Figure 3A to 3D are schematic cross-sections of a pallet and a tooth of an escape wheel illustrating the interaction according to the present invention.
Figure 4 and 5 show top-side etching and back-side etching using a Bosch DRIE process.

Elements in different embodiments that are similar or identical or that perform a similar or identical function are referred to by the same reference number.
Figures 1 and 2 show a monolithic oscillator 1 in a movement (not shown) comprising a substantially disc-shaped mass 2 that comprises two halves 2A, 2B that are com-pliantly interconnected by a set of flexures 3. Each of the halves is connected to a ground 4 by means of a plurality of further flexures, i.c. two radially extending flexures 5, four flexures in total, enabling the mass to oscillate. In the present example, the oscillator has a natural frequency in a range from 20 to 100 Hz, e.g. 40 Hz, and an amplitude in a range from 3° to 10° (in each direction, i.e. both in the CW direction and in the CCW direction), e.g. 5°.
Each of the halves 2A, 2B is provided with an anchor tooth 8, traditionally known as pallet. Further, the halves define an aperture that accommodates an escapement wheel 9 comprising a plurality of teeth 10. During oscillation, the anchor teeth on the oscillator alternately block and release the teeth of the escape wheel.
Figure 3A shows one of the anchor tooth 8 and an escape wheel tooth 10 in cross-section just prior to impulse, i.e. just prior to contact between the escape wheel and the oscillator and energy being transferred from the escape wheel to the oscillator. The escape wheel 10 and the oscillator 1 including the anchor teeth 8 are made from a silicon disc having parallel upper and lower surfaces and were shaped by DRIE. The sides of the escape wheel and the oscillator extend at a slight inclination, e.g. at an angle β of 89,6° with the top surfaces of the escape wheel and the oscillator. I.e. the teeth of the escape wheel and the anchor teeth have inclined end surfaces 8A, 10A that define a edge 8B, 10B with the respective top surfaces. Seen in top view, these edges 8B, 10B define the circumference of the teeth.
In Figure 3A, the circumferential edges of the escape wheel teeth and the anchor teeth are perfectly aligned (at exactly the same height, relative to the base plate of the movement). In practice, a watch movement is subjected to i.a. changes in orientation and shock which may result in temporary misalignment of the edges which in turn introduces inconsistency in the transfer of energy from the escape wheel to the oscillator. Figures 3B to 3D show various way of reducing or preventing such misalignment.
In Figures 3B and 3C, the angle β is reduced e.g. to 88° and the circumferential edges on the teeth of the escape wheel are located at least 50 µm, e.g. 200 µm removed from the upper surfaces of the anchor teeth. In addition, in Figure 3C, the angle of the end surfaces 10A of the teeth of the escape wheel is much smaller, e.g. 82° (Figure 3C shows an even smaller angle for illustrative purposes). This results in a larger angle, in this example 10°, between the end surface(s) of the escape wheel tooth and the end surface(s) of the anchor tooth, reducing electrostatic forces between the end surfaces of the teeth. In Figure 3D the circumferential edges on the teeth of the escape wheel are defined by a double taper.
The tapered angle described above can be achieved by, for instance:

a. Top-side etching using Bosch or other DRIE process, shown in Figure 4, and creating negative slope larger than 0.5 deg by manipulating process parameters such as increasing the etch gas flow, time, etch pressure, power temperature, decreasing passivation gas flow, decreasing passivation time, or any other combination of these or other process parameters.
b. Backside etching using Bosch or other DRIE process, shown in Figure 5, and creating a positive taper angle bigger than 0.5 deg by manipulating process parameters such as decreasing the etch gas flow, time, etch pressure, power temperature, increasing passivation gas flow, increasing passivation time, or any other combination of these or other process parameters.
c. Backside etching using any isotropic etching method
d. Backside etching using positively tapered masking layer with combination of (a), (b) or (c) and transferring the taper into semiconductor material.

The tapered mask can be created by:

i. Wet etching of the hard mask
ii. Using grayscale lithography on the photoresist masking layer
iii. Reflowing the photoresist masking layer
iv. Combining (i) or (ii) with dry etching of hard mask layer
v. Any combination above

The invention is not limited to the described embodiments and can be varied within the scope of the claims. For instance, the surfaces defining the circumferential edges could be e.g. curved, e.g. concave or convex. Also, the anchor teeth can be integrated in the flexures nearest the escape wheel, similar to what is described in NL 2024076 .

Claims

Movement for a watch, which movement comprises an escape wheel (9) having a plurality of teeth (10) and an oscillator (1) having anchor teeth (8), which anchor teeth (8) are controlled by the oscillator (1) to alternately block and release the teeth (10) of the escape wheel (9), wherein at least the escape wheel and the anchor teeth (10, 8) share an imaginary plane (P), characterized in that at least some of the teeth (10) of the escape wheel (9) and/or at least one of the anchor teeth (8) of the oscillator (1) comprises two surfaces defining a circumferential edge (10B, 8B) that is aligned with the end surfaces (8A, 10A) of the teeth (8, 10) of the other.
Movement according to claim 1, wherein the end surfaces (10A, 8A) of the teeth (10) of the escape wheel (9) and/or of the anchor teeth (8) define circumferential edges (10B, 8B) with the upper or lower surfaces of the escape wheel teeth (10) and/or anchor teeth (8).
Movement according to claim 2, wherein the edges (8B, 10B) having an angle smaller than 89,5°, preferably smaller than 89°, preferably smaller than 88°.
Movement according to any one of the preceding claims, wherein the escape wheel teeth (10) and anchor teeth (8) are configured such that during impulse and at the point of contact or line of contact the angle between the end surface (10A) of the escape wheel tooth (10) and the end surface (8A) of the anchor tooth (8) is larger 1°, preferably larger than 3°, preferably larger than 5°, preferably larger than 10°.
Movement according to any one of the preceding claims, wherein the circumferential edges (10B) on the teeth (10) of the escape wheel (9) are located between the upper and lower surfaces of the anchor teeth (8) or vice versa.
Movement according to claim 5, wherein the circumferential edges (10B) on the teeth (10) of the escape wheel (9) are located at least 50 µm, preferably at least 75 µm, preferably at least 100 µm removed from the upper and lower surfaces of the anchor teeth (8) or vice versa.
Movement according to any one of the preceding claims, wherein the escape wheel (9), the oscillator (1) and/or the anchor teeth (8) have a thickness smaller than 700 µm, preferably smaller than 550 µm, e.g. in a range from 250 µm to 500 µm, and/or wherein the oscillator (1) and the anchor teeth (8) are monolithic.
Movement according to any one of the preceding claims, wherein the escape wheel (9), the oscillator (1) and/or the anchor teeth (8) are shaped by means of reactive ion edging, such as RIE or DRIE and are preferably made from silicon.
Movement according to any one of the preceding claims, wherein the escape wheel (9) has a torque of less than 300 nanoNewtonmeter, preferably less than 200 nNm, preferably less than 150 nNm.
Movement according to any one of the preceding claims, wherein the oscillator (1) has and/or the anchor teeth have an amplitude smaller than 30°, preferably smaller than 20°, preferably smaller than 15°, e.g. in range from 3° to 10°.
Movement according to any one of the preceding claims, wherein the oscillator (1) has a natural frequency of 15 Hertz (Hz) or higher, preferably 25 Hz or higher, preferably 35 Hz or higher.
Movement according to any one of the preceding claims, wherein the oscillator (1) and the anchor teeth (8) are integral, e.g. monolithic, and form together with the escape wheel (9) a deadbeat escapement.
Movement according to any one of the preceding claims, comprising a base, wherein the oscillator (1) comprises a ground (4) that is mounted to the base and an oscillatory mass (2) that is suspended to the ground (4) via one or more elastic links (5), and/or wherein the escape wheel (9) s rotatably mounted to or in the base.
Movement (21) according to claim 13, comprising an energy storage and a gear train to transmit torque and energy to the escape wheel.
Wristwatch (20) comprising a movement (21) according to any one of the preceding claims.