PIEZOELECTRIC ROTARY PISTON MOTOR FOR DISC

Description

Scope of the invention

[0001] The invention relates to the technical field of rotary piezoelectric motors. Background of the invention

[0002] A rotary piezoelectric motor typically comprises a passive element and an actuator that rotates the passive element using the piezoelectric effect. With reference to the figure 1In particular, rotary piezoelectric motors 10 are known, in which the passive element 20 comprises a cylinder and the piezoelectric actuator comprises a resonator 30 including a pair of arms 31, 32 connected to each other at a connection zone 33, substantially in the shape of a tuning fork or a U. The piezoelectric actuator further comprises two piezoelectric elements (not shown), each attached to one of the arms 31, 32, and acting as excitation means for the arms to induce vibrations. The passive element 20 passes between the arms 31, 32 of the resonator. More specifically, a region of the lateral surface of the passive element 20 is in contact on both sides with the free ends 310, 320 of the arms 31, 32, so that the passive element 20 is set in rotation by friction of the free ends 310, 320 of the arms 31, 32 on the contact region.

[0003] In certain applications, particularly watchmaking applications, it would be desirable for the previously described piezoelectric actuator to be able to rotate a disk rather than a cylinder.

[0004] US patent 6,323,578 B1 describes a rotary piezoelectric motor comprising a piezoelectric actuator with a two-armed resonator connected at one end, the free ends rubbing against a passive disk to drive the disk into rotation. Summary of the invention

[0005] The aim of the present invention is to propose a rotary piezoelectric motor for which the piezoelectric actuator comprises a resonator having a pair of arms and the passive element comprises a disc that can be driven in rotation by said actuator.

[0006] In this regard, according to a first aspect, the invention relates to a rotary piezoelectric motor according to claim 1.

[0007] A disc is defined as a round, solid or hollow element. Examples include a date disc, a lunar phase disc, etc.

[0008] Such a motor has few components, is compact, and allows a high rotational speed of the disc thanks to a high available torque.

[0009] According to the present invention, the rim has a radial cross-section substantially in the shape of a U such that each of the two arms of the U rests on the free end of one arm. In other words, the rim has a fold.

[0010] This allows a pre-stress (also called preload) to be applied to the interface between the piezoelectric actuator and the passive element, to fix the holding torque without powering the motor, i.e. without exciting the arms.

[0011] According to a second aspect, the invention relates to an assembly comprising at least two piezoelectric motors according to the first aspect, the disks of the passive elements of the piezoelectric motors being concentric, superimposed and of different diameters, each disk except the one with the smallest diameter covering the disks of smaller diameter.

[0012] It is understood that the resonators of the active elements are positioned at different distances from the axis of the discs but in the same plane: this makes it possible to rotate several discs without it being cumbersome. A position detection system can be easily integrated, guaranteeing synchronization of the discs at all times.

[0013] According to a third aspect, the invention relates to a timepiece comprising a piezoelectric motor or a set of at least two piezoelectric motors as detailed above.

[0014] In a non-limiting embodiment, the timepiece includes a hand fixed to one end of the cylindrical part. Brief description of the drawings

[0015] Other features and advantages will become clear from the description given below, which is indicative and in no way exhaustive, with reference to the attached drawings, in which: there figure 1 The diagram, already described, schematically represents part of a rotary piezoelectric motor according to the prior art, in which the element to be driven in rotation is a cylinder, the figure 2 schematically represents part of a rotary piezoelectric motor according to a first embodiment of the invention, in which the element to be driven in rotation is a disk, the figure 3 schematically represents an area of ​​the rotary piezoelectric motor of the figure 2 , viewed in radial longitudinal section, the figure 4schematically represents a resonator of a rotary piezoelectric motor according to a second embodiment of the invention, the figure 5 schematically represents a set of rotary piezoelectric motors such as that of the figure 2 , seen in radial longitudinal section. Detailed description of preferred embodiments

[0016] A rotary piezoelectric motor according to the invention comprises a passive element including a disc 40, and a piezoelectric actuator enabling the disc 40 to be rotated using the piezoelectric effect.

[0017] In a first embodiment of the invention described with reference to figures 2 and 3The piezoelectric actuator comprises piezoelectric excitation means (not shown) and a resonator 30 including two oscillating arms 31, 32. The excitation means advantageously consist of two parts, each attached to a different arm. However, other embodiments of the excitation means are possible; for example, they may consist of a single part positioned at a joint between the arms. When a suitable voltage is applied to the excitation means, the means deform, and mechanical stresses are transmitted to the arms 31, 32, causing them to oscillate. By appropriately designing and mounting the excitation means on the arms, multidimensional oscillations of a desired shape can be achieved.

[0018] The arms 31 and 32 are connected at a connection point 33 and extend substantially parallel to each other from said connection point 33. The resonator 30 therefore has an overall tuning fork shape, that is, a U-shape. However, other shapes are possible. The ends of the arms not connected to the connection point 33 are called free ends 310 and 320. The amplitude of the oscillations of the arms 31 and 32 is maximum at these ends 310 and 320.

[0019] The passive element further comprises a rim 50 extending around the entire circumference of the disk 40. The rim 50 is formed of two parts: a first part connected to the disk 40, and a second part connected only to the first part. Together, the first and second parts form a circular groove surrounding the disk 40. In other words, the rim 50 has a U-shaped cross-section, according to a radial longitudinal section of the passive element, and the disk 40 is connected to one end of the U. The arm of the U connected to the disk 40 is referenced as 51, and the other arm of the U is referenced as 52.

[0020] The rim 50 passes locally between the free ends 310, 320 of the arms 31, 32. More precisely, the arm 51 presses against the free end 310 of the arm 31, and the arm 52 presses against the free end 320 of the arm 32, thus creating a radial prestress between the resonator 30 and the passive element, the radial term referring to a radius of the disk 40.

[0021] It is understood that the multidimensional oscillations of the free ends 310, 320 of the arms 31, 32 make it possible to impose a rotation on the disk 40 around its axis by friction of said ends 310, 320 against the rim 50.

[0022] It should be noted that in the embodiment presented to the figure 2The resonator 30 extends orthogonally to the disk 40, meaning that the plane containing the axes of the arms 31 and 32 of the resonator 30 is parallel to the plane defined by the disk 40. However, all technically possible inclinations of the resonator 30 relative to the disk 40 are conceivable. Naturally, the smaller the inclination, the thinner the piezoelectric motor, which is crucial in watchmaking.

[0023] Furthermore, the resonator is not limited to a U-shape or a tuning fork shape. In particular, in a second embodiment described with reference to the figure 4The arms may not be straight. Such a 30° resonator comprises two arms 31°, 32°. Said arms 31°, 32° are connected at a connection zone 33°. Each arm 31°, 32° comprises a main branch 311°, 321°, a free end 310°, 320°, and a connecting zone 312°, 322° allowing the main branch 311°, 321° and the free end 310°, 320° to be connected.

[0024] The main branches 311°, 321° extend substantially parallel to each other from said connection zone 33°. The connection zone 33° and the two main branches 311°, 321° are at the same level, that is to say the axes of the connection zone 33° and the axes of the two main branches 311°, 321° are contained in the same plane.

[0025] The free ends 310°, 320°, on the contrary, extend at a different level, and the plane containing the axes of the free ends 310°, 320° is parallel to the plane of the main branches 311°, 321° mentioned in the preceding paragraph. In the embodiment shown in the figure 3 The 312° and 322° connecting zones each include a portion extending orthogonally to the main branches 311° and 321° so as to bring the free ends 310° and 320° to a different level than that of the main branches 311° and 321°. However, the 312° and 322° connecting zones could very well be of another shape, the important thing being that the resonator comprises two stages.

[0026] The free ends 310° and 320° extend in each other's direction and face each other, and the rim 50 passes between said free ends 310° and 320°. More precisely, the arm 51 presses against the free end 310° of the arm 31°, and the arm 52 presses against the free end 320° of the arm 32°. The piezoelectric actuator includes piezoelectric excitation means, not shown. The excitation means advantageously consist of two parts, each attached to one of the free ends 310° and 320°. When a suitable voltage is applied to the excitation means, the excitation means deform, and mechanical stresses are transmitted to the free ends 310° and 320°, which then begin to oscillate. By appropriately designing and mounting the excitation means on the arms, multidimensional oscillations of the desired shape can be achieved.The multidimensional oscillations of the free ends 310°, 320° of the arms 31°, 32° allow a rotation to be imposed on the disk 40 around its axis by friction of said ends 310°, 320° against the rim 50.

[0027] For example, disc 40 is fixed in rotation to a needle 90, as shown for example in the figure 2 This makes the piezoelectric motor according to the invention particularly suitable for watchmaking components, due to its simplicity and compactness. The disc could alternatively be a date disc, a moon phase disc, or any type of disc used in watchmaking.

[0028] There figure 5 shows a set of 101 piezoelectric motors such as the one described with reference to figures 2 and 3 , although their resonators could very well be of the type described in reference to the figure 4Each motor comprises a 30, 30', 30" resonator and a passive element. Each 30, 30', 30" resonator comprises a first arm 310, 310', 310" and a second arm 320, 320', 320". Each passive element comprises a 40, 40', 40" disc and a 50, 50', 50" rim.

[0029] The discs 40, 40', 40" are concentric and superimposed. The discs 40, 40', 40" are of different diameters such that each disc 40', 40" covers a disc of smaller diameter 40, 40', except for the disc with the smallest diameter 40. Each rim 50, 50', except for the rim 50" adjacent to the disc with the largest diameter 40", is covered by a disc with a larger diameter 40', 40" than the one to which the rim 50, 50' is adjacent, so that the groove it defines is covered by said disc with the largest diameter 40', 40". It is clear that with such an arrangement, the rims 50, 50', 50" do not interfere with each other.

[0030] Each resonator 30, 30', 30" locally pinches the associated rim 50, 50', 50". In the embodiment presented in the figure 4 The resonators 30, 30', 30" are placed next to each other, that is to say at the same angular position relative to the discs 40, 40', 40". However, nothing prevents them from being placed at different angular positions relative to each other.

Claims

1. Rotating piezoelectric motor (100) including: - a piezoelectric actuator comprising a resonator (30) having a pair of arms (31, 32) connected at one of their ends in a connection area (33), the other two ends (310, 320) being referred to as 'free', - a passive element able to be driven in rotation by the friction of the free ends (310, 320) on the passive element, the passive element comprising a disc (40) and a rim (50) extending from the periphery of the disc (40), the rim (50) passing between the free ends (310, 320) of the arms (31, 32), the rim (50) having a substantially U-shaped radial cross-section such that each of the two branches (51, 52) of the U rests on the free end (310, 320) of an arm (31, 32).

2. Timepiece including a piezoelectric motor (100) according to the preceding claim.

3. Timepiece according to the preceding claim, comprising a hand (90) integral in rotation with the disc (40).

4. Assembly (101) comprising at least two piezoelectric motors according to any of the preceding claims, the discs (40, 40', 40") of the passive elements of the piezoelectric motors being concentric, superposed and of different diameters, each disc (40', 40"), except the disc of smallest diameter, covering the discs of smaller diameter (40, 40').

5. Timepiece including an assembly according to the preceding claim6. Timepiece according to the preceding claim, comprising at least two hands such that each disc (40, 40', 40") is integral in rotation with one of the hands.