Balance, timepiece movement, timepiece and manufacturing method of balance

1. A balance comprising:

a balance staff pivotally supported rotatably; and

a balance wheel arranged around the balance staff and in which one end portion is a fixed end portion fixed to a connection arm which is radially connected to the balance staff and the other end portion is a free end portion which can be radially deformed;

wherein the balance wheel has a first rim which is connected to the connection arm and a second rim which is arranged to be overlapped with the first rim and formed of a material having a linear expansion coefficient different from the first rim;

wherein the first rim and the second rim are arranged in a circumferential direction and are bonded together by a plurality of melting portions formed of melted materials of the first and second rims, the plurality of melting portions being formed on upper and lower surfaces of and in an intermediate position between the first and second rims.

2. The balance according to claim claim 1 , wherein the balance wheel has a first arcuate section and a second arcuate section which are circumferentially divided around the balance staff; and wherein an interval spaced between the plurality of melting portions in the first arcuate section is different from an interval spaced between the plurality of melting portions in the second arcuate section.

3. The balance according to claim 1 , wherein one of the melting portions is continuously formed in a circumferential direction on a bonding surface between the first rim and the second rim.

4. The balance according to claim 1 , wherein the second rim is arranged to be overlapped with an outer periphery of the first rim, and wherein the plurality of melting portions are formed apart from each other on a bonding surface between the first rim and the second rim.

5. A timepiece movement comprising:

a barrel wheel having a power source;

a train wheel which transmits a rotational force of the barrel wheel; and

an escapement mechanism which controls rotation of the train wheel;

wherein the escapement mechanism includes the balance according to claim 1 .

6. A timepiece comprising: the timepiece movement according to claim 5 .

7. The balance according to claim 1 , wherein the balance wheel comprises a rim divided along a circumferential direction thereof into a plurality of belt-shaped pieces each formed of the first and second rims bonded together by the plurality of melting portions.

8. A balance comprising:

a balance staff pivotally supported rotatably; and

a balance wheel arranged around the balance staff and in which one end portion is a fixed end portion fixed to a connection arm which is radially connected to the balance staff and the other end portion is a free end portion which can be radially deformed;

wherein the balance wheel has a first rim connected to the connection arm and a second rim arranged to be overlapped with the first rim and formed of a material having a linear expansion coefficient different from the first rim;

wherein the first rim and the second rim are bonded together by a plurality of melting portions in which respective materials thereof are melted;

wherein the balance wheel has a first arcuate section and a second arcuate section which are circumferentially divided around the balance staff; and

wherein an interval spaced between the plurality of melting portions in the first arcuate section is different from an interval spaced between the plurality of melting portions in the second arcuate section.

9. A balance comprising:

a balance staff pivotally supported rotatably; and

a balance wheel comprised of a plurality of arcuate sections each connected by a connection arm to the balance staff, each of the arcuate sections having first and second rims bonded together by a plurality of melting portions formed of melted materials of the first and second rims.

10. The balance according to claim 9 , wherein each of the arcuate sections has a fixed end portion connected to the connection arm and a free end portion configured to be radially deformed.

11. The balance according to claim 9 , wherein the material of the second rim has a linear expansion coefficient different from the material of the first rim.

12. The balance according to claim 9 , wherein the plurality of melting portions are formed on upper and lower surfaces of and in an intermediate position between the first and second rims.

13. The balance according to claim 9 , wherein second rim is arranged to be overlapped with an outer periphery of the first rim; and wherein the plurality of melting portions are formed apart from each other on a bonding surface between the first and second rims.

14. The balance according to claim 9 , wherein for each of the arcuate sections, the plurality of melting portions are spaced at an interval along circumferential directions of the first and second rims.

15. The balance according to claim 14 , wherein the spacing interval for the plurality of melting portions of one of the arcuate sections is different from the spacing interval of the plurality of melting portions for each of the other of the arcuate sections.

16. The balance according to claim 9 , wherein for each of the arcuate sections, one of the melting portions is continuously formed in a circumferential direction on a bonding surface between the first and second rims.

17. A timepiece movement comprising:

a barrel wheel having a power source;

a train wheel for transmitting a rotational force of the barrel wheel; and

an escapement mechanism having the balance according to claim 9 for controlling rotation of the train wheel.

18. A timepiece comprising the timepiece movement according to claim 17 .