HK1205286B - Silicon overcoil balance spring - Google Patents
Silicon overcoil balance spring Download PDFInfo
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- HK1205286B HK1205286B HK15105483.6A HK15105483A HK1205286B HK 1205286 B HK1205286 B HK 1205286B HK 15105483 A HK15105483 A HK 15105483A HK 1205286 B HK1205286 B HK 1205286B
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Description
Technical Field
The invention relates to a silicon-based end-coil balance spring. In particular, the invention relates to silicon end coil hairspring springs and methods of manufacturing such springs.
Background
The regulating assembly of a timepiece generally comprises a balance, which is an inertial flywheel, and a balance spring, which is a resonator. These two components determine the quality of operation and the precision of the timepiece. The resonant frequency of the balance spring and balance system controls the operation and regulation of the movement of the timepiece.
The use of silicon as a material for the manufacture of balance springs is known in the field of clock springs. Due to advances in the development of the IC industry, the ultra-high manufacturing accuracy of such manufacturing processes provides a high accuracy in the dimensions of the balance spring. Furthermore, silicon is a non-magnetic material, which provides advantages in the manufacturing process of the timepiece.
It is known that the coils of a planar balancing spring deform eccentrically when the balancing spring is operating, which results in the center of gravity of the balancing spring not corresponding to the center of rotation of the balance wheel and the balancing spring. This changes the setting of the balance and balance spring and results in unsynchronized movement.
Although the center of gravity of the balance spring can be arbitrarily returned to the center by being shifted, this does not solve this disadvantage. Since during operation of the balancing spring the centre of gravity will move, this will no longer coincide with the initial centre of gravity.
Different solutions have been proposed in the prior art to reduce the above-mentioned drawbacks and to make the deformations of the balancing spring coils more concentric.
Examples of such prior art include:
(i) a Breguet end-turn balance spring with a so-called Philips curve, in which the outer curve is lifted into a second plane above the balance spring, and
(ii) schtelman (Straumann) double balance spring, in which two balance springs manufactured as a matched pair are arranged so that they oscillate biased in opposite directions to each other, in order to eliminate or reduce such effects.
A first example (i) is directed to modifying an initial planar balancing spring such that it becomes a balancing spring that occupies multiple planes. Breguet has produced Breguet (Breguet) end coil balance springs from silicon based materials, whereby the balance spring is formed from two or more parts as an assembled end coil balance spring.
A second example (ii) consists of two balancing springs, which are made as matched pairs. They are arranged to oscillate biased in opposite directions to each other such that as they oscillate, the centers of gravity of the two springs move outwardly and inwardly on opposite symmetrical paths so as to maintain the cumulative centers of gravity of the two springs towards the center of the spindle. However, this results in more energy consumption because there are two balancing springs in this oscillating system.
Disclosure of Invention
The present invention aims to provide a balancing spring that overcomes or minimises at least some of the disadvantages that are exhibited by balancing springs such as those of the prior art.
In a first aspect, the invention provides a method of producing a silicon balance spring of one piece construction having a last coil spring portion for adjusting a mechanical timepiece, the method comprising the steps of:
(i) providing a silicon balance spring having a body portion and an outer portion for forming into a last coil spring portion, wherein the outer portion extends radially outwardly from an outermost turn of the body portion, and wherein the body portion and the outer portion are integrally formed of a silicon-based material and are formed in a coplanar configuration;
(ii) moving the outer portion in a direction relative to and away from the plane of the body portion and in a direction towards the plane passing through and towards the body portion; and
(iii) (iii) providing a stress relaxation process to the counterbalance spring to relieve internal stresses induced within the counterbalance spring from step (ii);
wherein the outer portion is positioned in a last coil hairspring configuration relative to the body portion after the outer portion is moved into the plane of the body portion.
The movement of step (ii) may occur incrementally in a direction towards a plane passing through and towards the body portion. Step (iii) may be caused to occur between or during the incremental steps of step (ii).
Preferably, an oxidation step of at least the outer portion occurs before step (ii) occurs to remove or minimise stress concentration defects. Preferably, the oxidation step comprises exposure to a solution of hydrogen fluoride.
The method may comprise the step of twisting an outer portion by at least one 180 ° turn, wherein the at least one 180 ° turn surrounds a longitudinal axis of the outer portion, and wherein the outer portion is twisted in a region adjacent to the outer turn of the body portion.
Preferably the stress relaxation process is carried out at a temperature exceeding 500 ℃, more preferably at a temperature exceeding 700 ℃ and even more preferably at a temperature exceeding 1100 ℃.
Preferably the stress relaxation process is carried out for at least 10 hours, more preferably at least 20 hours, and even more preferably at least 30 hours.
Preferably the balance spring is formed by micro-fabrication techniques, more preferably by Deep Reactive Ion Etching (DRIE) techniques.
In a second aspect, the invention provides a silicon balance spring when formed in one piece with a last coil spring portion according to the first aspect.
Preferably, the balance spring is sized to fit on a timepiece.
In a third aspect, the present invention provides a silicon-based balancing spring comprising:
a body part having a spring arrangement for providing a restoring torque for adjusting the mechanical timepiece, an
A final coil spring portion, wherein the final coil spring portion extends in a direction relative to and away from the plane of the body portion and in a direction towards a plane passing through and towards the body portion;
wherein the body portion and the last coil hairspring portion are integrally formed.
The balancing springs are preferably formed by micro-fabrication techniques, and more preferably by Deep Reactive Ion Etching (DRIE) techniques.
Drawings
Preferred embodiments of the invention will be described in further detail below by way of example and with reference to the accompanying drawings, in which:
figures 1a and 1b depict perspective and top views of one embodiment of a balance spring according to the present invention before the formation of the final coil spring arrangement;
figures 2a and 2b depict perspective and top views of an embodiment of the balance spring of figures 1a and 1b with a partially configured final coil spring arrangement;
figures 3a and 3b depict perspective and top views of the embodiment of the balance spring of figures 2a and 2b with a further partially configured final coil spring arrangement;
figures 4a and 4b depict perspective and top views of the embodiment of the balance spring of figures 1a to 3b with a fully configured final coil spring arrangement;
FIGS. 5, 6, 7, 8 and 9 depict the formation of the balancing spring of FIGS. 1a to 4 b; and
fig. 10 depicts an SEM image of a cross-sectional view of a coil turn of a balance spring according to the present invention.
Figure 11a depicts a top view of a further embodiment of a balance spring according to the invention before formation of the final coil spring arrangement;
FIG. 11b depicts a perspective view of an embodiment of the balance spring of FIG. 11a with a partially configured last coil spring arrangement;
11c and 11d depict top and side views of the embodiment of the balance spring of FIGS. 11 a-11 b with a fully configured final coil spring arrangement;
figure 12a depicts a top view of another embodiment of a balance spring according to the invention before formation of the final coil spring arrangement;
FIG. 12b depicts a perspective view of an embodiment of the balance spring of FIG. 12a with a partially configured last coil spring arrangement;
fig. 12c and 12d depict top and side views of the embodiment of the balance spring of fig. 12 a-12 b with a fully configured final coil spring arrangement.
Detailed Description
The present invention provides a planar silicon balance spring having a body and an integrally formed last coil spring portion to improve the concentricity and isochronism of such a spring when used in a timepiece.
The balance spring includes a final coil spring portion thereof which achieves said improvements in concentricity and isochronism, said final coil spring portion being formed integrally with the body of the balance spring and extending from the periphery of the body of the balance spring in an out-of-plane final coil spring arrangement and by the manufacturing process used for its formation.
The present invention provides a method of manufacturing a final balance spring, whereby the balance spring is formed from a silicon based material, which provides a silicon final balance spring formed integrally without the need for any connection units as required for the previously mentioned silicon final balance spring manufactured by Breguet (Breguet), US 7950847.
According to the present invention there is provided a balance spring formed from a silicon based material, whereby the balance spring comprises a body portion and a last coil hairspring portion.
The balance spring is initially formed and provided with the portions in a coplanar form and is formed by micro-fabrication techniques including photolithography and Deep Reactive Ion Etching (DRIE), whereby the body portion, collet portion and end coil spring portion are coplanar.
With the technique and process according to the invention as described below and as described with reference to the accompanying drawings, the said last coil spring portion is provided out of the plane and in accordance with the last coil spring portion of the balance spring as used to increase the concentricity of the balance spring, but without involving the mechanical integrity of the balance spring and without having to abut a separate last coil spring portion onto the body portion.
According to the invention, the shape and configuration of the parts of the balance spring can be modified by using thermal techniques without compromising the necessary mechanical properties of the balance spring as required during use in a timepiece.
In the present invention there is provided a method for producing an integrally formed silicon balance spring having a final coil spring portion and a spring produced therefrom, whereby the balance spring is initially formed, said balance spring having a main body portion for providing a restoring torque to adjust the spring arrangement of a mechanical timepiece, and an outer portion for forming the final coil spring portion, wherein said outer portion extends radially outwardly from the outermost turn of the main body portion. The body portion and the outer portion are integrally formed from a silicon-based material and are formed in a coplanar configuration.
The outer portion is moved in a direction relative to the body portion and away from the plane of the body portion and in a direction towards the plane passing through and towards the body portion.
A stress relaxation process is provided to the balance spring to relieve internal stresses induced within the balance spring, and the outer portion is positioned in a final coil spring configuration relative to the body portion after the outer portion moves into the plane of the body portion.
Embodiments and examples of the present invention are described below.
With reference to the embodiment as depicted in fig. 1a to 4b, the original balance spring 2, as shown in fig. 1a and 1b, has a body portion 23 and an outer portion 22 before the last coil spring portion is formed in a twisting motion, and it has a "C" shaped twisted area 21. The balance spring 2 is thus provided in an initial planar configuration, and the outer portion 23 and the body portion 23 are integrally formed of a single material and are coplanar. The radius R1 of the twisted region is slightly smaller than the radius R2 of the second outermost coil. This design helps the torsion area 21 of the final end-turn balance spring to follow the archimedean spiral (from a top view).
As shown in fig. 2a, 2b, 3a, 3b, 4a and 4b, the shape change of the balance spring 2 is depicted to form a last coil spring portion, whereby the shape change takes place by moving the outer portion in a direction relative to and away from the plane of the body portion and in a direction towards the plane passing through and towards the body portion to form a last coil spring portion, causing a gradual twisting of the outer portion 22 away from the body portion.
After the outer part 22 is moved towards the plane of the spring body, the depicted original balance spring 2 shape is transformed into a final balance spring, as shown in fig. 4a and 4b, the outer part 22 is twisted at 180 ° relative to the outermost turn of the body of the adjacent spring thereby forming a final balance spring part.
Other related embodiments of other geometries of the balancing spring according to the invention are discussed below.
Referring to figures 5 to 9, there is depicted the manner in which the balance spring of figures 1a to 4b can be manipulated in accordance with the invention to provide a single formed end coil balance spring.
In order to achieve the movement and twisting process of the balancing spring 2, it is necessary to grip the body part 23 and the outer part 22 with the holders 61, 62. In the present embodiment, the outer portion 22 of the balance spring 2 needs to be turned 180 °, and this process requires high positioning accuracy.
For the design of this embodiment, two holders are provided as required for maintaining the position accuracy, as shown in fig. 5 to 9. The first holder 61 serves to hold all the central coils of the main body portion 23 of the balance spring 2 except for the outer portion 22 including the outer portion as the "C" -shaped twisted region 21, and the second holder 62 serves to hold the outer portion 22 of the balance spring 2.
In the present embodiment, both holders 61, 62 are formed of silicon by DRIE and oxidized by thermal oxidation. The first holder 61 for holding the central coil of the main body portion 23 of the balancing spring 2 is made with a series of grooves almost identical to the coils of the main body portion 23 of the balancing spring 2. The groove is provided with a width slightly larger than the line width of the balance spring coil. This can help the center coil of the balance spring body portion 23 maintain its original shape when a torque is applied to the torsion region 21.
The second holder 62 for holding the outer portion 22 is likewise provided with a groove sized so as to accommodate the coil outer portion. The same process as the first holder 61 is applied on the second holder 62.
During the course of movement, all turns except the twisted area 21 need to be fixed by the holder. As shown in fig. 6, the central coil of the main body portion 23 of the balance spring 2 and the outer portion 22 are respectively installed into the first holder 61 and the second holder 62, and the balance spring is then moved according to the description of the present invention.
Figures 6, 7, 8 and 9 progressively depict the movement of the formation of the last-coil hairspring portion. After moving the balance spring into the final coil hairspring shape as shown in fig. 9, the balance spring is transferred into an annealing furnace together with a holder.
To achieve a final coil balance spring with low internal stress, a high temperature and long duration anneal is preferred, if the sample is placed in a furnace without N2 or Ar protection, the temperature should be below the oxidation temperature of silicon to avoid sticking of the balance spring to the holder, and a temperature of 800 ℃ is suitable for this application. After cooling, the original balance spring 2 is provided as a last coil balance spring.
For different balancing spring sizes and sizes, there may be cases where the torsion region 21 of the balancing spring 2 cannot withstand a large torsion angle. In these cases, the annealing process may be provided in incremental steps, where the movement of the outer portion of the balancing spring is accomplished in several steps.
After positioning the balancing spring 2 into the two holders 61, 62 as shown in fig. 6, the balancing spring outer portion 22 is twisted 60 ° as shown in fig. 7 and subsequently annealed with the annealing conditions discussed below.
After the first anneal, the balance spring 2 changes to a twisted configuration, as shown in fig. 2. A second further 60 ° twist is then applied to the twisted balancing spring 2, as shown in fig. 7, and subsequently annealed.
This annealing process produces a further distorted balancing spring 2, as shown in fig. 2. The final remaining 60 ° twist is applied to the twisted balance spring 2 after the two previous annealing processes, as shown in fig. 8.
The balancing spring 2 and the holders 61, 62 are then transferred into a furnace for final annealing. After removal of the holders 61, 62, the silicon balance spring 2 is permanently transformed into a last-coil balance spring.
Silicon is a brittle material at room temperature, however at temperatures between 520 ℃ and 600 ℃, silicon follows a transition from brittle to ductile properties. At temperatures above 700 c, it has been found that the necessary amount of plastic deformation is possible.
Although this embodiment describes incremental movement through the outer portion of the body portion, this may be continuous movement in other embodiments, which may include incremental or continuous heat treatment.
According to the invention and with reference to the embodiments described above and also applicable to the other or alternative embodiments as described below with reference to fig. 11a to 12d, the silicon balance spring is prepared prior to the oxidation process of the DRIE (deep reactive ion etching) etched silicon balance spring 2, the outer part of the balance spring is twisted onto another plane and it is fixed by using a quartz jig.
The oxidation temperature is preferably about 1100 deg.c and is held constant for about 30 hours. After the oxidation process, it was confirmed that the shape of the outer portion of the balance spring was changed to a preset shape by the quartz jig.
To confirm that the shape change was not due to an oxide layer, the balance spring was immersed in a Hydrogen Fluoride (HF) solution. When the oxide layer is removed from the surface of the balance spring, the shape of the balance spring remains the same as when oxidized.
Thus, it could be confirmed that the crystal structure was changed during the oxidation process, which resulted in permanent shape change.
The following calculations demonstrate this mechanism and stress with reference to the stress induced during movement and twisting of the outer portion of the balancing spring.
To simplify the calculation of the twist angle and the shear stress, the outer part of the balancing spring to be twisted will be considered as a straight beam, with beam widths t and h and beam length l.
The twist angle Φ is a function of the shear modulus G, the polar moment of inertia Ip, the torque Mt exerted on the beam, and the beam length l. We found Φ as Mt·l/G·Ip。
In the distortionThe maximum shear stress in the beam during the period is τ ═ 3Mt/h·t2。
The relationship between Φ and τ can then be found, τ being 3 Φ · G · Ip/l·h·t２。
In beams having rectangular cross-section, the polar moment of inertia is Ip＝K·h·t3Where K is a constant related to the ratio of h/t.
We found τ to be 3K · Φ · G · t/l, and we found K to be 0.249, taking h to be 2.5t to 100 μm, l to 5mm, G to 69GPa as an example.
Thus, for a given parameter of the beam, the maximum stress is τ -400 Φ (MPa).
For a twist angle of 180 deg., the maximum stress inside the balance spring coil is about 1.3 GPa. According to Pearson et al (Pearson) (4.1957, 4 th, volume 5, pages 181 to 191), the breaking stress of a thinner silicon rod at room temperature is about 3 GPa.
Furthermore, the silicon twist scan mirror manufactured by IBM (IBM journal of research and development (IBM j. res. develop), No. 5, vol. 24, pages 631 to 637, p. 9, 1980) also demonstrated that, as manufactured and tested by researchers, a thinner silicon rod can withstand a larger breaking stress, and that this value was found to be such that the balance spring was strong enough to withstand a 180 ° twist.
Preferably, an oxidation treatment is used before the movement/twisting of the outer part of the balancing spring is completed.
During oxidation, oxygen atoms penetrate through a previously formed oxide layer to react with silicon atoms to form silicon oxide. At the sharp corners of the balancing spring, this penetration occurs more easily due to the relatively large surface area and thus a thicker oxide layer is created, which smoothes the interface of silicon and silicon oxide.
Further embodiments of the present invention are shown and described with reference to fig. 11a to 11d, and another embodiment of the present invention is shown and described with reference to fig. 12a to 12 d.
A further embodiment of a balancing spring 111 having a main body portion 112 and an outer portion 113 is shown in fig. 11a to 11 d. In this embodiment similar to fig. 1a to 4b, but with the outer portion 113 having the opposite twist sense. As for the embodiment shown in fig. 1a to 4b having a "C" shaped 180 ° twisted area, the outer portion 113 is twisted away from the plane of the main portion 112 and away from the paper. In contrast, however, with the "S" -shaped 180 ° twisted region in the present embodiment, the outer portion 113 is twisted toward the sheet and into the sheet.
Another embodiment of a balancing spring 121 having a body portion 122 and an outer portion 123 is depicted in fig. 12a to 12 d. The original counter spring 121 before twisting is shown in fig. 12a, having one twisted area and one bent area. After twisting and raising the outer portion 123 away from and towards the plane of the paper, the outer portion 123 is bent over the body portion 122 to form the shape of the last coil balance spring.
It will be appreciated by those skilled in the art that there are other and alternative embodiments of the balance spring of the present invention whereby the configuration of the outer part relative to the body part may be varied and the pattern of movement of the outer part away from and past the body part may be varied to form the final coil balance spring and thus the final coil balance spring, in addition to the exemplary embodiments depicted and described without departing from the scope of the present invention.
When immersed in an HF solution, the initial sharp corners of the silicon balancing spring are removed with an oxide layer, as can be seen in the SEM image of the cross-section of the oxidized silicon balancing spring in fig. 10.
As can be seen, where 11 is the silicon core, 12 is the oxide layer, the sidewall roughness has been greatly reduced, and the corners of the cross-section have been rounded.
The oxidation process performed prior to the large angle twist can remove defects generated by the DRIE process and sharp corners of the cross-section, which makes the balance spring more durable due to the reduction of stress concentration.
The present invention provides a balance spring having the following advantages:
(i) precision manufacturing;
(ii) a large amount of concentricity compensation;
(iii) a one-piece construction and no extra part required to be attached to the spring;
(iv) since there are no engaging parts and a constant cross-sectional area is possible, therefore:
a. a constant second area moment, and therefore a more uniform hardness;
b. a constant cross-sectional area and therefore an oxide layer is utilized to facilitate thermal compensation.
Claims (28)
1. A method of producing a silicon balance spring of one piece construction having a last coil spring portion for adjusting a mechanical timepiece, the method comprising the steps of:
(i) providing a silicon balance spring having a body portion and an outer portion for forming into a last coil spring portion, wherein the outer portion extends radially outwardly from an outermost turn of the body portion, and wherein the body portion and the outer portion are integrally formed of a silicon-based material and are formed in a coplanar configuration;
(ii) moving the outer portion in a direction relative to and away from a plane of the body portion and in a direction towards the plane passing through and towards the body portion; and
(iii) (iii) providing a stress relaxation process to the counterbalance spring so as to relieve the internal stress induced within the counterbalance spring from step (ii);
wherein the outer portion is positioned in a last coil hairspring configuration relative to the body portion after the outer portion moves into the plane of the body portion.
2. The method of claim 1, wherein the moving of the step (ii) occurs incrementally in a direction toward the plane passing through and toward the body portion.
3. The method of claim 2, wherein said step (iii) occurs between or during the incremental steps of step (ii).
4. The method of claim 1, wherein before step (ii) occurs, an oxidation step of at least the outer portion occurs to remove or minimize stress concentration defects.
5. The method of claim 2, wherein before step (ii) occurs, an oxidation step of at least the outer portion occurs to remove or minimize stress concentration defects.
6. A method according to claim 3, wherein before step (ii) occurs, an oxidation step of at least the outer portion occurs to remove or minimise stress concentration defects.
7. The method of claim 4, wherein the oxidizing step comprises exposure to a hydrogen fluoride solution.
8. The method of claim 5, wherein the oxidizing step comprises exposure to a hydrogen fluoride solution.
9. The method of claim 6, wherein the oxidizing step comprises exposure to a hydrogen fluoride solution.
10. The method of any of claims 1-9, further comprising the step of twisting the outer portion by at least one 180 ° turn, wherein the at least one 180 ° turn surrounds a longitudinal axis of the outer portion, and wherein the outer portion is twisted in a region adjacent to an outer turn of the body portion.
11. The method of any one of claims 1-9, wherein the stress relaxation process is performed at a temperature in excess of 500 ℃.
12. The method of any one of claims 1-9, wherein the stress relaxation process is conducted at a temperature in excess of 700 ℃.
13. The method of any one of claims 1-9, wherein the stress relaxation process is performed at a temperature in excess of 1100 ℃.
14. The method of any one of claims 1-9, wherein the stress relaxation process is performed for at least 10 hours.
15. The method of any one of claims 1-9, wherein the stress relaxation process is performed for at least 20 hours.
16. The method of any one of claims 1-9, wherein the stress relaxation process is performed for at least 30 hours.
17. The method of any of claims 1-9, wherein the balancing spring is formed by a microfabrication technique.
18. The method of any of claims 1-9, wherein the balancing spring is formed by a deep reactive ion etching technique.
19. The method of claim 10, wherein the stress relaxation process is conducted at a temperature in excess of 500 ℃.
20. The method of claim 10, wherein the stress relaxation process is conducted at a temperature in excess of 700 ℃.
21. The method of claim 10, wherein the stress relaxation process is conducted at a temperature in excess of 1100 ℃.
22. The method of claim 10, wherein the stress relaxation process is performed for at least 10 hours.
23. The method of claim 10, wherein the stress relaxation process is conducted for at least 20 hours.
24. The method of claim 10, wherein the stress relaxation process is conducted for at least 30 hours.
25. The method of claim 10, wherein the balancing spring is formed by a micro-fabrication technique.
26. The method of claim 10, wherein the balancing spring is formed by a deep reactive ion etching technique.
27. A monolithically formed silicon balance spring having a last coil hairspring portion formed in accordance with the method of any one of claims 1 to 26.
28. The integrally formed silicon counter spring of claim 27, wherein the counter spring is sized for use on a timepiece.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| HK15105483.6A HK1205286B (en) | 2013-07-29 | 2015-06-09 | Silicon overcoil balance spring |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| HK13108857.0 | 2013-07-29 | ||
| HK13108857.0A HK1193537A2 (en) | 2013-07-29 | 2013-07-29 | Silicon overcoil balance spring |
| HK15105483.6A HK1205286B (en) | 2013-07-29 | 2015-06-09 | Silicon overcoil balance spring |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| HK1205286A1 HK1205286A1 (en) | 2015-12-11 |
| HK1205286B true HK1205286B (en) | 2018-05-11 |
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