Balance spring with rhomboidal cross-section for a mechanical movement of a watch, and method for producing the balance spring

Abstract

The present invention relates to a balance spring for a mechanical movement of a watch, wherein the balance spring is embodied as a spiral spring and has a winding cross section. It is provided according to the invention that the winding cross section of the spiral spring is in the shape of a rhombus, wherein the rhombus has four sides, two first corners with a first internal angle, two second corners with a second internal angle, a first diagonal, connecting the two first corners to one another, and a second diagonal, connecting the two second corners to one another, the first diagonal being shorter than the second diagonal, and the first internal angle being larger than the second internal angle.

Claims

1. A balance spring for a mechanical movement of a watch, wherein the balance spring is embodied as a spiral spring and has a winding cross section, wherein the winding cross section of the spiral spring is in the shape of a rhombus, the rhombus having at least four sides, two first corners with a first internal angle α, two second corners with a second internal angle β, a first diagonal, connecting the two first corners to one another, and a second diagonal, connecting the two second corners to one another, wherein the first diagonal is shorter than the second diagonal, and wherein the first internal angle is larger than the second internal angle.

2. The balance spring according to claim 1, wherein the two second corners, which are connected to one another by the second diagonal, are cut parallel to the first diagonal, so that the rhombus has two additional sides.

3. The balance spring according to claim 2, wherein the distance between the two additional sides is between 0.05 mm and 0.2 mm.

4. The balance spring according to claim 2, wherein the two additional sides have a length between 0.01 mm and 0.05 mm.

5. The balance spring according to claim 2, wherein the length of the first diagonal is between 0.03 mm and 0.07 mm.

6. The balance spring according to claim 2, wherein the second internal angle β is between 3° and 30°.

7. The balance spring according to claim 6, wherein the second internal angle β is between 10° and 30°.

8. The balance spring according to claim 2, wherein the transition between the two additional sides and the respective adjacent sides of the rhombus is curved, the radius (R) of the curve being between 0.005 mm and 0.05 mm.

9. The balance spring according to claim 1, wherein the winding cross section is designed to be symmetrical with respect to the first diagonal of the rhombus as well as with respect to the second diagonal of the rhombus.

10. The balance spring according to claim 1, wherein the balance spring is made of a ceramic material.

11. The balance spring according to claim 10, wherein the ceramic material comprises a glass ceramic.

12. The balance spring according to claim 2, wherein the winding cross section is designed to be symmetrical with respect to the first diagonal of the rhombus as well as with respect to the second diagonal of the rhombus.

13. The balance spring according to claim 2, wherein the balance spring is made of a ceramic material.

14. The balance spring according to claim 13, wherein the ceramic material comprises a glass ceramic.

15. A movement for a watch comprising: a spiral spring having a winding cross section, wherein the winding cross section of the spiral spring is in the shape of a rhombus, the rhombus having at least four sides, two first corners with a first internal angle α, two second corners with a second internal angle β, a first diagonal, connecting the two first corners to one another, and a second diagonal, connecting the two second corners to one another, wherein the first diagonal is shorter than the second diagonal, and wherein the first internal angle is larger than the second internal angle.

16. A method for manufacturing a balance spring, wherein the balance spring is embodied as a spiral spring and has a winding cross section, wherein the balance spring is manufactured from an unmachined part, wherein the unmachined part is made of a ceramic material and is structured by means of a selective laser ablation method, such that the winding cross section of the spiral spring is in the form of a rhombus, the rhombus having at least four sides, two first corners with a first internal angle α, two second corners with a second internal angle β, a first diagonal, connecting the two first corners to one another, and a second diagonal, connecting the two second corners to one another, the first diagonal being shorter than the second diagonal, and the first internal angle being larger than the second internal angle.

17. The method according to claim 16, wherein the unmachined part is a disk.

18. The method according to claim 16, wherein the unmachined part has a thickness of 0.1 mm to 0.25 mm.

19. The method according to claim 16, wherein a first V-shaped groove is created by means of a laser on a first side of the unmachined part, wherein a second V-shaped groove is also created by means of a laser on the opposite second side of the unmachined part, such that the first and second grooves are situated congruently one above the other and together form an opening, which separates individual windings of the spiral spring from one another.

20. The method according to claim 16, wherein an ultrashort pulse laser is used to carry out the selective laser ablation method.

Description

(1) One embodiment of the present invention is explained in greater detail below with reference to the drawings.

(2) The drawings show:

(3) FIG. 1: an embodiment of a balance spring according to the invention in a view from above,

(4) FIG. 2: the winding cross section of the balance spring according to the invention from FIG. 1 according to sectional line II marked in FIG. 1,

(5) FIG. 3: a detailed view of a corner of the cross-sectional profile from FIG. 2,

(6) FIG. 4: an unmachined part in the form of a disk, from which the balance spring according to the invention is produced, in an oblique view,

(7) FIG. 5: the disk from FIG. 4 after creating a V-shaped groove in the top side of the disk,

(8) FIG. 6: a section through the disk from FIG. 5 along sectional line VI from FIG. 5, and

(9) FIG. 7: the section from FIG. 6 showing the second groove with dashed lines on the bottom side of the disk.

(10) In the following discussion, the same parts are labeled with the same reference numerals. If a figure contains reference numerals that are not explained in detail in the description of the respective figure, reference is made to the previous description of a figure or to the next.

(11) FIG. 1 shows a top view of one embodiment of a balance spring 1 according to the invention. The spiral shape of the balance spring can be seen clearly in this view.

(12) The winding cross section of the balance spring 1 is the same over the entire length of the spring body. A sectional plane II has been drawn in FIG. 1 merely as an example. The respective winding cross section is shown in FIG. 2. As indicated by this figure, the winding cross section 2 is essentially in the form of a rhombus. The basic shape of the rhombus has four sides 3, two first corners 4 with a first internal angle α, two second corners 5 with an internal angle β, a first diagonal 6, connecting the two first corners to one another, and a second diagonal 7, connecting the two second corners to one another. The first diagonal 6 of the basic shape is shorter than the second diagonal 7.

(13) The actual winding cross section is obtained only by cutting off the two second corners 5 parallel to the first diagonal 6. The actual winding cross section therefore has a total of six sides, not just four. The two additional sides resulting from cutting the basic rhomboid body are labeled with reference numeral 8 in the drawing.

(14) According to the invention, the distance 9 between the two additional sides 8 advantageously amounts to between 0.05 mm and 0.2 mm. The two additional sides 8 also preferably have a length between 0.01 mm and 0.05 mm. The length of the first diagonal is also preferably between 0.03 mm and 0.07 mm. The second internal angle β is also preferably between 3° and 30°. In the embodiment shown here, the second internal angle is approximately 30°.

(15) To simplify production of the balance spring according to the invention, the transition between the two additional sides 8 and the respective adjacent sides 3 of the rhombus is curved. The radius R of the curve is between 0.005 mm and 0.05 mm, as can be seen clearly in FIG. 3.

(16) In the embodiment shown here, the two second opposing corners 5 are each cut at the same height, resulting in a winding cross section that is designed to be symmetrical with respect to the first diagonal 6 and also with respect to the second diagonal 7.

(17) The method of producing the balance springs according to the invention is described below. The balance spring is manufactured from an unmachined part, which is made of a ceramic material. An unmachined part made of a glass ceramic is preferably used.

(18) The unmachined part is a circular disk 10, which is shown in an oblique view in FIG. 4. The disk 10 is structured by means of a selective laser ablation method, so as to yield the desired winding cross section. To do so, a first V-shaped groove 13 is first created in the top side 16 of the disk 10 by the laser beam 12 of an ultrashort pulse laser 11. The groove 13 can be seen in FIG. 5 as well as in the sectional diagram in FIG. 6. The V-shaped groove 13 marks the interspace between the subsequent windings of the balance spring and is therefore designed as a spiral itself. As shown in FIG. 6, the depth of the groove amounts to slightly more than half the thickness of the material of the disk 10. In FIG. 6, the base of the groove is therefore below line 15, which marks the center of the ceramic disk 10.

(19) After the first groove 13 has been created in the top side 16 of the disk 10, the disk 10 is turned over, so that the bottom side 17 of the disk can be structured with the laser 11. Then a V-shaped groove is also created in the bottom side 17 by means of the laser. This second V-shaped groove is indicated with dashed lines in FIG. 7 and is labeled with reference numeral 14. The two V-shaped grooves 13 and 14 are congruent and together form an opening that separates the individual windings of the spiral balance spring from one another.