Piezoelectric element for an automatic frequency control circuit, oscillating mechanical system and device comprising the same

Patent metadata

Field	Value
Publication number	US-10969745-B2
Application number	US-201816112817-A
Country	US
Kind code	B2
Filing date	Aug 27, 2018
Priority date	Sep 14, 2017
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

A piezoelectric element for an automatic frequency control circuit. The element includes a balance spring formed of a piezoelectric crystal strip, a first electrode connected to the automatic control circuit, and disposed on at least a first side of the strip, and a second electrode connected to the automatic control circuit and disposed on at least a second side of the strip. The first and second electrodes are placed on one portion or over the entire length of the balance spring in a predetermined angular distribution.

First claim

What is claimed is:

1. A piezoelectric element for an automatic frequency control circuit, the piezoelectric element comprising:
a balance spring formed of a strip of piezoelectric material;
a first electrode, intended to be connected to the automatic frequency control circuit, and disposed on at least a first side of the strip of piezoelectric material;
a second electrode, intended to be connected to the automatic frequency control circuit, and disposed on at least a second side of the strip of piezoelectric material;
wherein the piezoelectric material is a piezoelectric crystal or a piezoelectric ceramic;
wherein the first and second electrodes are placed on one portion or over the entire length of the balance spring in a predetermined angular distribution,
wherein the first and second electrodes are disposed on one portion of an outer coil of the balance spring, said portion including one end of the balance spring and defining a predetermined angular sector, and
wherein the first electrode includes first portions disposed on the first side of the strip of piezoelectric material and second portions disposed on at least one side of the strip of piezoelectric material distinct from the first side; wherein the second electrode includes first portions disposed on the second side of the strip of piezoelectric material and second portions disposed on at least one side of the strip of piezoelectric material distinct from the second side; the first and second portions of the first electrode respectively the second electrode being alternately connected to each other in junction areas; and wherein said junction areas are distributed over the balance spring with a predetermined angular periodicity.

2. The piezoelectric element according to claim 1 , wherein the second portions of the first electrode and the second portions of the second electrode are disposed on a third side of the strip of piezoelectric material; and wherein said second portions of the first and second electrodes extend in succession and alternately one after the other on the third side of the strip of piezoelectric material, with said predetermined angular periodicity.

3. The piezoelectric element according to claim 2 , wherein the electrodes are disposed over the entire length of the balance spring.

4. The piezoelectric element according to claim 1 , wherein the element includes a third electrode and a fourth electrode; the third electrode being connected to the first electrode in a first connection terminal intended to be connected to the automatic frequency control circuit, the third electrode including first portions disposed on a third side of the strip of piezoelectric material and second portions disposed on at least one side of the strip of piezoelectric material distinct from the third side; the fourth electrode being connected to the second electrode in a second connection terminal intended to be connected to the automatic frequency control circuit, the fourth electrode including first portions disposed on a fourth side of the strip of piezoelectric material and second portions disposed on at least one side of the strip of piezoelectric material distinct from the fourth side; the first and second portions of the third electrode respectively the fourth electrode being alternately connected to each other in junction areas; and wherein said junction areas are distributed over the balance spring with said predetermined angular periodicity.

5. The piezoelectric element according to claim 4 , wherein each second portion of the first, second, third, respectively fourth electrode extends over every side of the strip of piezoelectric material distinct from the first, second, third, respectively fourth side; and wherein the first, second, third and fourth electrodes extend in succession and alternately one after the other on each side of the strip of piezoelectric material, with a predetermined angular sub-periodicity.

6. The piezoelectric element according to claim 5 , wherein the predetermined angular sub-periodicity encompasses an arc of the balance spring that is substantially equal to 60°.

7. The piezoelectric element according to claim 1 , wherein the piezoelectric crystal is a single crystal.

8. The piezoelectric element according to claim 7 , wherein the piezoelectric crystal is a single crystal chosen from the group consisting of topaz, berlinite, lithium niobate, lithium tantalate, gallium phosphate, gallium arsenate, aluminium silicate, germanium dioxide, a single crystal tourmaline, a single crystal from the group of zinc blende structure III-V semiconductors, or a single crystal from the group of wurtzite structure II-VI semiconductors.

9. The piezoelectric element according to claim 7 , wherein the piezoelectric crystal is single crystal quartz.

10. The piezoelectric element according to claim 9 , wherein the balance spring is machined in Z-cut single crystal quartz.

11. The piezoelectric element according to claim 1 , wherein the predetermined angular sector encompasses an arc of the balance spring that is substantially equal to 60°.

12. The piezoelectric element according to claim 1 , wherein the element further includes at least one groove made in the first upper or lower side of the strip of piezoelectric material, said first electrode being at least partially disposed in said groove, said second electrode being at least partially disposed on a second outer or inner side.

13. The piezoelectric element according to claim 12 , wherein the groove is concave.

14. An oscillating mechanical system for an automatic frequency control circuit, comprising a balance and a piezoelectric element provided with a balance spring, the balance spring being mounted on said balance, wherein the piezoelectric element conforms to claim 1 .

15. A device comprising the oscillating mechanical system according to claim 14 and a circuit for automatic control of the oscillation frequency of the oscillating mechanical system, said automatic control circuit including an oscillator stage able to provide a reference signal, means for comparing the frequency of two signals, and a frequency adaptation unit connected to the piezoelectric element of the oscillating mechanical system and able to provide a frequency adaptation signal, wherein the piezoelectric element of the oscillating mechanical system is able to generate an alternating voltage at a frequency matching the oscillating mechanical system, the first and second electrodes of the piezoelectric element being connected to the automatic control circuit in order to receive the frequency adaptation signal from the frequency adaptation unit, on the basis of the result of a frequency comparison, in the frequency comparison means, between the alternating voltage and the reference voltage.

16. The device according to claim 15 , wherein the circuit for automatic control of the oscillation frequency of the oscillating mechanical system further includes a rectifier for rectifying the alternating voltage generated by the piezoelectric element and for storing the rectified voltage across at least one capacitor, in order to supply the automatic control circuit with electricity.

17. The device according to claim 15 , wherein the oscillator stage of the automatic control circuit includes an oscillating circuit connected to a MEMS resonator to provide an oscillating signal, so that the oscillator stage provides the reference signal, all the electronic components of the automatic control circuit being grouped together to form a single electronic module.

18. The piezoelectric element ac

Assignees

• Swatch Group Res & Dev Ltd

Inventors

• Haemmerli Alexandre
• Gueissaz Francois
• Tombez Lionel
• Schnyder Bernhard
• Dalla Piazza Silvio

Classifications

• G04B17/227

  composition and manufacture of the material used (composition and manufacture of hairsprings G04B17/066; of springs G04B1/145; anti-magnetic alloys G04B43/007; ferrous alloys C22C; non-ferrous alloys C22C, B22F) · CPC title

• G04B17/066

  Manufacture of the spiral spring (locking of the spiral spring by the regulating lever G04B18/026; spiral spring with temperature compensation G04B17/227; fixation of the spiral spring on the collet G04B17/32; mainspring G04B1/14) · CPC title

• H03H9/02023

  consisting of quartz · CPC title

• G04C3/047 Primary

  using other coupling means, e.g. electrostrictive, magnetostrictive · CPC title

• H03H2003/0414

  Resonance frequency · CPC title