Process for producing a thermo-compensated oscillator

1 . A process for manufacturing a timepiece oscillator comprising a balance and at least two spring portions that are arranged in parallel, wherein the process consists of the following performed in the order provided:

a. choosing the frequency f of the oscillator;

b. choosing the balance and the at least two spring portions, by selecting the most appropriate distinct spring portions among at least two batches or at least two sets of existing spring portions, so that the inertia of the balance and the angular stiffnesses of the spring portions allow an oscillator of chosen frequency f to be formed and so that the variations in angular stiffness of the spring portions as a function of temperature are able to thermo-compensate the oscillator; and

c. assembling said chosen at least two spring portions to form a spring, which is in its turn assembled with the chosen balance, said spring comprising a parallel arrangement of two spirals, an attachment of each of the two spirals being on the one hand to the arbor of the balance, and, on the other hand, to the balance bridge,

wherein the distinct spring portions are not integrally formed.

2 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the process comprises choosing the materials of the balance and of the spring portions prior to the choosing the frequency, the choosing the balance and spring portions, and the assembling.

3 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the choosing the balance and spring portions comprises choosing a balance of inertia I and spring portions, each spring portion i of angular stiffnesses C i , that respect the following equations:

f

=

1

2

⁢

π

⁢

∑

i

⁢

C

i

I

⁢

and

⁢

1

f

⁢

df

dT

=

1

2

⁢

(

∑

i

⁢

C

i

(

CTE

i

+

3

⁢

α

s

,

i

)

∑

i

⁢

C

i

-

2

⁢

α

bal

)

=

0

,

wherein CTE i is the thermal coefficient of the Young's modulus of the spring portion i, α s,i is the thermal expansion coefficient of the spring portion i, α ba1 is the thermal expansion coefficient of the balance, and T is temperature,

wherein each spring portion i is a spiral or spiral segment, and i is a number from 1 to n, wherein n is the total number of spring portions.

4 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the balance is made of CuBe2.

5 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the choosing the balance and spring portions comprises selecting at least two spring portions having variations in their angular stiffness Ci of opposite signs as a function of temperature.

6 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the spring portions are made of at least one material selected from the group consisting of single-crystal silicon whatever its crystal orientation, polysilicon, amorphous silicon, quartz, amorphous silicon oxide, doped silicon whatever the dopant type and concentration, alloys based on Fe—Ni possessing a positive CTE, and Nb—Zr—O alloys.

7 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the spring portions have a shape of a turn segment, of one or more turns, of rectilinear blades, or of a combination of at least one turn segment and at least one turn, at least one turn segment and at least one rectilinear blade, at least one turn and at least one rectilinear blade, or at least one turn segment, at least one turn and at least one blade.

8 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the choosing the balance and spring portions comprises:

choosing the inertia I for the balance; then

choosing the balance, which inertia is equal or close to the chosen value I; then

determining the angular stiffnesses Ci for each portion i of the spring so that

f

=

1

2

⁢

π

⁢

∑

i

⁢

C

i

I

and that the following equation also equals zero

1

f

⁢

df

dT

=

1

2

⁢

(

∑

i

⁢

C

i

(

CTE

i

+

3

⁢

α

s

,

i

)

∑

i

⁢

C

i

-

2

⁢

α

bal

)

=

0

;

then

choosing the spring portions whose respective angular stiffnesses are within +/−10% of the angular-stiffness values C i ,

wherein CTE i is the thermal coefficient of the Young's modulus of the spring portion i, α s,i is the thermal expansion coefficient of the spring portion i, α ba1 is the thermal expansion coefficient of the balance, and T is temperature,

wherein each spring portion i is a spiral or spiral segment, and i is a number from 1 to n, wherein n is the total number of spring portions.

9 . The process for manufacturing an oscillator as claimed in claim 1 , wherein the choosing the balance and spring portions comprises:

choosing the balance and measuring or estimating its the inertia I; then

determining the angular stiffnesses C i for each portion i of the spring so that

f

=

1

2

⁢

π

⁢

∑

i

⁢

C

i

I

and that the following equation also equal zero

1

f

⁢

df

dT

=

1

2

⁢

(

∑

i

⁢

C

i

(

CTE

i

+

3

⁢

α

s

,

i

)

∑

i

⁢

C

i

-

2

⁢

α

bal

)

=

0

;

then

choosing the spring portions whose respective angular stiffnesses are within +/−10% of the angular-stiffness values C i ,

wherein CTE i is the thermal coefficient of the Young's modulus of the spring portion i, α s,i is the thermal expansion coefficient of the spring portion i, α ba1 is the thermal expansion coefficient of the balance, and T is temperature,

wherein each spring portion i is a spiral or spiral segment, and i is a number from 1 to n, wherein n is the total number of spring portions.

10 . A timepiece oscillator manufactured using a process as claimed in claim 1 , wherein the oscillator comprises the balance and the return spring comprising the at least two spring portions that are arranged in parallel.

11 . The oscillator as claimed in claim 10 , wherein at least two of the spring portions have variations in their angular stiffness Ci of opposite signs as a function of temperature.

12 . The oscillator as claimed in claim 10 , wherein the oscillator comprises at least two spring portions made of materials selected from the group consisting of single-crystal silicon whatever its crystal orientation, polysilicon, amorphous silicon, quartz, amorphous silicon oxide, doped silicon whatever the dopant type and concentration, alloys based on Fe—Ni possessing a positive CTE, and Nb—Zr—O alloys.

13 . The oscillator as claimed in claim 10 , wherein the at least two distinct portions have the shape of spiral springs, of turns, of rectilinear blades, or of a combination of at least one spiral spring and at least one turn, at least one spiral spring and at least one rectilinear blade, at least one turn and at least one rectilinear blade, or at least one spiral spring, at least one turn and at least one rectilinear blade.

14 . The oscillator as claimed in claim 10 , wherein the oscillator comprises at least one distinct portion that has a cross section that varies over a length of the distinct portion.

15 . The oscillator as claimed in claim 10 , wherein the oscillator includes at least two distinct portions, which are arranged in parallel, comprising blades located in a same plane.

16 . The oscillator as claimed in claim 10 , wherein the oscillator comprises an angular return spring including at least two distinct portions that are arranged in parallel and wherein the oscillator comprises at least two attachments to the balance arbor and/or at least two attachments to the frame of the timepiece movement.

17 . A timepiece wherein the timepiece is a watch and comprises an oscillator as claimed in claim 10 .

18 . The oscillator as claimed in claim 11 , wherein the oscillator comprises at least two spring portions made of materials selected from the group consisting of single-crystal silicon whatever its crystal orientation, polysilicon, amorphous silicon, quartz, amorphous silicon oxide, doped silicon whatever the dopant type and concentration, alloys based on Fe—Ni possessing a positive CTE, and Nb—Zr—O alloys.

19 . The oscillator as claimed in claim 11 , wherein the at least two distinct portions have the shape of spiral springs, of turns, of rectilinear blades, or of a combination of at least one spiral spring and at least one turn, at least one spiral spring and at least one rectilinear blade, at least one turn and at least one rectilinear blade, or at least one spiral spring, at least one turn and at least one rectilinear blade.

20 . The process for manufacturing an oscillator as claimed in claim 1 , wherein one or more of the spring portions have a cross section that varies over a respective length thereof.