Rotary piezoelectric motor, especially for watchmaking

Abstract

The invention relates to a rotary piezoelectric motor (1), in particular for a timepiece, the motor (1) comprising: - a rotor (3) configured to be able to rotate and actuate a mechanical device, - a stator (2) configured to rotate the rotor (3), the stator (2) comprising a piezoelectric actuator provided with a resonator (29) arranged to perform an oscillating movement, the stator (2) comprising a fixed element (4) and the resonator comprising a movable element (5) arranged at a distance from the fixed element (4) and connected to the fixed element (4), the piezoelectric actuator being configured to move the movable element (5) against the rotor (3) to rotate the rotor (3), the movement of the movable element (5) rotating the rotor (3) in a first direction.

Description

Technical Field

[0001] This invention relates to the technical field of rotary piezoelectric motors. It also relates to the technical field of timepieces equipped with such rotary piezoelectric motors. Technical Background

[0002] The electric motors commonly used in the watchmaking industry are "Lavet" type rotary motors, which operate based on the principles of electromagnetic physics. Typically, this type of motor includes a stator with windings and a magnetized rotor, which rotates by phase shifts in the windings.

[0003] However, these motors have limited resistance to strong magnetic fields. Starting with a given magnetic field value, the motors lock. Typically, they lock under magnetic fields exceeding 2 mT.

[0004] Therefore, to avoid this problem, it is necessary to design motors that operate based on other physical principles.

[0005] For example, there are electrostatic motors with comb teeth, such as the electrostatic motor described in patent CH709512. However, these comb teeth take up a lot of space, and they consume more energy than "Lavet" type motors.

[0006] For example, a piezoelectric motor-based motor was developed in patent EP0587031. However, the latter is limited to date actuation. Its high energy consumption and risk of premature wear prevent it from driving the second hand, which typically requires even more energy. Summary of the Invention

[0007] The present invention aims to provide a rotary piezoelectric motor that can withstand high electromagnetic fields while maintaining appropriate energy consumption and size.

[0008] Therefore, the present invention relates to a rotary piezoelectric motor, particularly for use in timepieces, the motor comprising: - A rotor, configured to rotate and actuate mechanical devices. - A stator configured to rotate a rotor, the stator including a piezoelectric actuator having a resonator arranged to perform a oscillating motion.

[0009] The significant feature of this invention is that the stator includes a fixed element, and the resonator includes a movable element arranged at a distance from the fixed element and connected to the fixed element, and the piezoelectric actuator is configured to move the movable element against the rotor to rotate the rotor, the movement of the movable element causing the rotor to rotate in a first direction.

[0010] Because of the piezoelectric actuator, the stator with this configuration can easily transmit rotational motion to the rotor. In fact, the movable element can move to contact the rotor, thereby transmitting motion in the first direction. Therefore, when the resonator oscillates, the movable element contacts the rotor and transmits a force to it, causing it to rotate in the first direction.

[0011] According to a specific embodiment of the invention, the resonator includes at least one flexible arm, preferably two flexible arms, and possibly three or four flexible arms, which are connected at one end to a fixed element of the stator and at the other end to a movable element of the stator, preferably angularly distributed around the movable element.

[0012] According to a specific embodiment of the present invention, when the movable element contacts the rotor, the movable element performs track motion in a second direction opposite to the first direction.

[0013] According to a specific embodiment of the invention, the movable element is always in contact with the rotor during motor operation.

[0014] According to a specific embodiment of the invention, the movement of the movable element causes the rotor to rotate continuously.

[0015] According to a specific embodiment of the present invention, the movable element cannot rotate or move on its own.

[0016] According to a specific embodiment of the invention, the movable element has an annular shape, and the rotor is arranged inside the annular shape.

[0017] According to a specific embodiment of the invention, the contact between the movable element and the movable rotor is within a ring.

[0018] According to a specific embodiment of the invention, the rotor includes a toothed wheel, and the ring includes an internal gear system that engages with the external gear system of the toothed wheel.

[0019] According to a particular embodiment of the invention, the arm performs a radial reciprocating motion, causing the movable element to swing and move.

[0020] According to a particular embodiment of the invention, the movable element is arranged around the rotor.

[0021] According to a specific embodiment of the invention, the arm is phase-shifted between two consecutive arms. The signal is actuated, and N is the number of arms.

[0022] According to a particular embodiment of the invention, the resonator oscillates at a frequency corresponding to its inherent frequency.

[0023] According to a specific embodiment of the invention, the motor includes means for constantly or temporarily adjusting the mechanical tension of each arm by means of a DC bias voltage or by means of changing the amplitude of an AC voltage.

[0024] According to a specific embodiment of the invention, the rotor and / or stator are obtained by micromachining, for example, by being made of silicon or metal.

[0025] According to a specific embodiment of the invention, the rotor includes flexible blades to maintain gear transmission with the movable element in the event of an impact.

[0026] The present invention also relates to a timepiece including a watch movement comprising a gear transmission configured to rotate at least one hand, and the timepiece further comprising a piezoelectric motor arranged to actuate the gear transmission. Attached Figure Description

[0027] Referring to the accompanying drawings, for indicative and non-limiting purposes, other features and advantages will become apparent from the following description, wherein: Figure 1 A schematic top view of a first embodiment of the rotary piezoelectric motor according to the invention at rest is shown, with the rotor and stator not in contact. Figure 2 A schematic top view of a first embodiment of a rotary piezoelectric motor according to the invention is shown in operation, with the rotor and stator in contact at the 6 o'clock position. Figure 3 A schematic top view of a first embodiment of the rotary piezoelectric motor according to the invention is shown in operation, with the rotor and stator in contact at the 9 o'clock position. Figure 4 A schematic top view of a first embodiment of a rotary piezoelectric motor according to the invention is shown in operation, with the rotor and stator in contact at the 12 o'clock position. Figure 5 A schematic top view of a first embodiment of the rotary piezoelectric motor according to the invention is shown in operation, with the rotor and stator in contact at the 3 o'clock position. Figure 6 A bottom view of a first embodiment of the rotary piezoelectric motor according to the present invention at a stop is schematically shown. Figure 7 A schematic cross-sectional side view of a rotary piezoelectric motor according to a first embodiment of the present invention is shown. Figure 8 The diagram schematically shows a top view of a second embodiment of the rotary piezoelectric motor according to the invention at rest, with the rotor and stator not in contact. Figure 9 A bottom view schematically illustrates a second embodiment of a rotary piezoelectric motor according to the present invention. Figure 10 The diagram schematically illustrates a top view of a third embodiment of the rotary piezoelectric motor according to the invention in operation, with the motor subjected to an impact, and... Figure 11 It is a graph that shows the acceleration caused by the impact on the piezoelectric motor and the motion of the toothed wheel. Detailed Implementation

[0028] Figures 1 to 7 This illustrates a first embodiment of the rotary piezoelectric motor 1. Specifically, the motor can be used in a timepiece to actuate a display device (such as a pointer arranged on a dial). The piezoelectric motor 1 extends substantially in a plane.

[0029] The piezoelectric motor 1 includes a rotor 3, which is self-rotating and movable, and is configured to rotatably and actuate a mechanical gear transmission, particularly for display devices. The piezoelectric motor 1 includes a stator 2, which is configured to actuate the rotor 3 and cause it to rotate.

[0030] The rotor 3 includes a toothed wheel 9 arranged at the center of the piezoelectric motor 1. For example, the wheel 9 is mounted on a shaft 13, which has pivots 15 at each end, these pivots being mounted in bearings 16 to allow the shaft 13 to rotate. The wheel 9 includes an outer ring 28 and a central hub 27, the hub 27 being connected to the ring 28 by rigid pins 19. The shaft 13 includes a pinion 21 parallel to the wheel 9, the pinion 21 being arranged to transmit motion received by the wheel 9 to a gear transmission 17, such as to the movement of a timepiece. The wheel 9 has a peripheral gear train 10 on the ring 28, which allows the wheel 9 to be actuated.

[0031] Preferably, the rotor 3 and / or the stator 2 comprises silicon, and more preferably, entirely comprises silicon. Alternatively, when the stator 2 is made of silicon, the rotor 3 is made of metal to limit wear and friction, and vice versa.

[0032] Alternatively, the rotor 3 and / or stator 2 may preferably be entirely composed of materials such as quartz, nickel (obtained by metal electrodeposition or LIGA-type process) or diamond (obtained by ALD-type deposition) through micromachining.

[0033] The stator 2 includes a fixed element 4 and a movable element 5, which is configured to actuate the wheel 9 of the rotor 3. The movable element 5 is arranged at a certain distance from the fixed element 4. The movable element 5 has an annular shape arranged around the rotor 3, which is arranged inside the annulus. The movable element 5 has an internal gear train 12 on the annulus, which engages with the peripheral gear train 10 of the toothed wheel 9 to rotate it. The annulus is larger than the rotor 3 so that the rotor 3 can be inserted.

[0034] The fixed element 4 has a shape that forms a circular internal space, and the movable element 5 and the rotor 3 are arranged in the circular internal space.

[0035] The stator 2 also includes a piezoelectric actuator 25 incorporated into the resonator to perform a oscillating motion, thereby generating orbital motion at the movable element 5. The resonator includes the movable element 5 and is connected to the fixed element 4.

[0036] The resonator includes three flexible arms 6, 7, and 8, which are connected at one end to a fixed element 4 of the stator 2 and at the other end to a movable element 5 of the stator 2. The flexible arms 6, 7, and 8 are distributed at an angle around the movable element 5. Therefore, for the three arms 6, 7, and 8, two consecutive arms are arranged at an angle of 120°.

[0037] Alternatively, according to other embodiments, the piezoelectric actuator includes a resonator with two arms, and may also have four arms. With two arms, the angle is 180°, while with four arms, the angle is 90°.

[0038] The piezoelectric actuator is configured to move the movable element 5 against the rotor 3, thereby rotating the rotor 3. Arms 6, 7, and 8 perform radial reciprocating motion so that the movable element 5 oscillates alternately in a substantially horizontal plane.

[0039] Preferably, arms 6, 7, and 8 are formed of a crystalline or polycrystalline material, such as silicon, and their thickness allows them to be deformed. The arms include piezoelectric material layers to enable electrical activation. Each arm 6, 7, and 8 includes two laterally juxtaposed piezoelectric material layers 23 and 24, each layer 23 and 24 connected to opposite polarities. Each layer 23 and 24 terminates on the fixing element 4 via a contact surface through which voltage is supplied to the layers 23 and 24 via a circuit not shown in the figure.

[0040] Therefore, by electrically activating the piezoelectric material layers 23 and 24, arms 6, 7, and 8 alternately deform laterally in the central and outward directions. Activation is generated using an alternating current voltage.

[0041] Preferably, the motor 1 includes means for adjusting the mechanical tension of each arm 6, 7, 8, particularly capable of centering the orbital movement around the rotor 3, or slightly altering the natural frequency of the motor 1. For example, the adjustment means is constant by means of a bias voltage. Alternatively, the adjustment means is temporary by means of means of changing the amplitude of the AC voltage.

[0042] Each arm 6, 7, 8 forms an approximately circular arc from the inner edge of the fixed element 4 to the outer edge of the movable element 5. This arc forms an angle greater than 180° and possibly greater than 250°. Therefore, each arm surrounds a portion of the movable element 5. Two consecutive arms 6, 7, 8 partially overlap. The lengths of arms 6, 7, 8 are chosen as a function of the distance the movable element 5 should cover.

[0043] Arms 6, 7, and 8 are actuated by alternating signals, which can be sinusoidal, square, or trapezoidal. The signals transmitted to arms 6, 7, and 8 undergo phase shifting between two consecutive arms. N is the number of arms.

[0044] Therefore, the three arms 6, 7, and 8 are simultaneously activated by signals with a 120° phase shift between two consecutive arms 6, 7, and 8. In the embodiment with two arms, the phase shift is 180°, while in the case of four arms, the phase shift is 90°, and so on.

[0045] The arms deform due to the deformation of the piezoelectric layer. Actuating arms 6, 7, and 8 perform alternating radial reciprocating motions by approaching and moving away from the center of the motor (i.e., rotor 3). The end connected to the fixed element 4 does not move, but the end connected to the movable element 5 moves the most. Therefore, the movable element 5 moves under the deformation of arms 6, 7, and 8.

[0046] The phase shift between arms 6, 7, and 8 causes the movable element 5 to move along its orbit, preferably in a circular motion. The movable element 5 performs this circular motion while remaining non-rotatable. Therefore, the rotational motion is transmitted to the rotor 3 in one direction, such as... Figure 2 As shown.

[0047] Preferably, the movement of the movable element 5 is continuous, causing the rotor 3 to rotate continuously. Therefore, the movable element 5 is always in contact with the rotor 3 during motor operation. The contact between the movable element 5 and the rotor 3 is movable within the ring.

[0048] Figures 2 to 5 The diagram shows the contact point P between the rotor 3 and the ring moving within the ring at different consecutive time points. The orbital motion of the ring (whose internal space is larger than that of the rotor 3) creates a movable contact point P between the ring and the rotor 3. At each time point, different portions of the ring's internal gear train 12 mesh with the peripheral gear train 10 of the toothed wheel 9. Therefore, the rotor 3 is driven to rotate.

[0049] exist Figure 2 In the middle, the movable element 5 is lifted, so that the contact point P is located at the bottom of the toothed wheel 9, i.e., at the 6 o'clock position. Figure 3 In the middle, the movable element 5 shifts to the right, so that the contact point P is on the left side of the toothed wheel 9, that is, at the 9 o'clock position. Then, the movable element 5 descends, so that the contact point P is at the top of the toothed wheel 9, that is, at the 12 o'clock position, as shown. Figure 4 As shown. Finally, in Figure 5 In the middle, the movable element 5 shifts to the left, so that the contact point P is to the right side of the toothed wheel 9, i.e., at the 3 o'clock position. From one figure to the next, the movable element 5 has performed a quarter revolution of orbital movement.

[0050] like Figure 1 As shown, when the movable element 5 rotates in the opposite direction, the movable element 5 moves away from the rotor 3 and is no longer in contact with the rotor 3. Therefore, the rotational motion is not transmitted to the rotor 3 in the other direction, and the rotor 3 rotates only in one direction.

[0051] For example, the tooth system 10 of rotor 3 includes 56 teeth, while the tooth system 12 of movable element 5 includes 60 teeth. Therefore, the reduction factor r between the contact point speed and the rotor speed is given by the following formula. Where Zm refers to the number of teeth of the movable element 5, and Zr refers to the number of teeth of the rotor 3. Therefore, in our example, This reduction is advantageous because it is directly integrated into the motor, thereby reducing the number of additional reduction gears required, for example, to drive the pointer.

[0052] Preferably, at least one tooth of the tooth system 10 of the rotor 3 contacts the tooth system 12 of the movable element 5 to transmit motion. This avoids the risk of the rotor 3 being locked. The dimensions of the movable element 5 and the rotor 3 can be determined such that only one tooth of the tooth system 10 contacts the tooth system 12 of the rotor 3.

[0053] Preferably, a DC voltage is applied individually to each arm 6, 7, 8 to move the swing center of the movable element 5 in order to compensate for possible natural eccentricity and thereby improve the efficiency of the motor 1.

[0054] Preferably, the amplitude of the AC voltage applied to arms 6, 7, and 8 that enables the movable element 5 to swing is variable, so that the swing of the movable element 5 is completely circular to compensate for the possible natural ellipticization of the trajectory, thereby also improving the efficiency of motor 1.

[0055] If it is desired to rotate rotor 3 in another direction, simply reverse the polarity of the voltage applied to the resonator. Therefore, the movement of arms 6, 7, and 8 causes the movable element 5 of stator 2 to rotate in the opposite direction. In the case of actuating an analog display, this allows the pointer position to be set in both directions.

[0056] In the case of the watch, the resonant frequency or natural frequency of motor 1 is adapted to the frequency of the quartz crystal used to set the operation of the movement. An excitation frequency corresponding to a divisor of the quartz frequency is selected, typically 32764 Hz. For example, a frequency of 128 Hz is chosen. Preferably, the frequency of motor 1 is adjusted and tuned using the excitation frequency so that its oscillation amplitude is not less than 90-95% of its maximum amplitude.

[0057] The frequency can be adjusted by changing the mass of the movable element 5 and / or the stiffness of the arms 6, 7, and 8. For example, a ring 18 can be fitted under the movable element 5 to reduce its weight, thereby reducing its oscillation frequency. For example, the ring 18 is made of nickel silver, preferably entirely of nickel silver.

[0058] To increase the frequency, the material can be made lighter, for example by laser or milling. Because these processes allow for very precise adjustment, they are preferred for use with quartz-tuned motors.

[0059] The magnitude of the motor's resonant peak coupled to its load should be high enough, i.e., much higher than the resonant peak of the quartz crystal. This is why the motor speed can be slightly altered by changing the motor's excitation frequency without losing too much amplitude, such as compensating for speed loss after shocks or any other disturbances, so that the quartz time base can be aligned with the pointer position again.

[0060] Figure 8 and Figure 9 A second embodiment of the piezoelectric motor 30, similar to the first embodiment, is shown. The difference lies in that the rotor 3 is equipped with a damping device. The wheel 9 of the rotor 3 includes flexible blades 49 connecting the ring 38 that carries the external gear train 40 and the hub 37. In this embodiment, the rotor 3 is provided with three flexible blades 49 distributed at an angle in the wheel of the rotor. Each of them forms a helical arc portion.

[0061] Therefore, if the motor 30 shakes violently, the flexible blades 49 absorb the impact applied to the rotor 3 through their deformation. The blades 39 are soft to avoid transmitting the impact to the shaft. Similar to the first embodiment, the shaft bearings may also include additional damping devices.

[0062] Figure 10 A third embodiment of the piezoelectric motor 50, similar to the second embodiment, is shown, in which an impact is applied to the fixing element 4 of the stator 2 during operation of the piezoelectric motor 50. This impact generates acceleration in the direction indicated by the arrow. This causes the movable element 5 to move X in the direction opposite to the arrow. m This causes it to detach from rotor 3. However, due to the deformation of the flexible blades 49 of rotor 3, rotor 3 also moves X in the same direction as movable element 5. r Therefore, rotor 3 remains in contact with movable element 5 so that gear transmission is maintained despite impacts. The mass of rotor 3 and the elasticity of flexible blades 49 enable rotor 3 to follow the same trajectory as movable element 5. Thus, gear transmission and track motion of movable element 5 are maintained.

[0063] exist Figure 11 In the graph, due to the horizontal impact applied from left to right, the acceleration Following the expression of acceleration The impact curve or wave. The movement X of the movable element 5. m and the motion X of rotor 3 r It follows the damping curve, which is a curve that follows the damping curve.

[0064] Advantageously, the masses of rotor 3 and movable element 5, the stiffness of flexible arm 49 of rotor 3 in the impact direction, and the stiffness of flexible arms 6, 7, and 8 of movable part 5 are selected to ensure that trajectory X m and X r coincide.

[0065] In this embodiment, the impact is applied along the X-axis. Of course, the impact can be applied in any direction in the X and Y planes while maintaining the gear transmission between the rotor 3 and the movable element 5.

[0066] Advantageously, the mass of rotor 3 and movable element 5, as well as the stiffness of flexible arm 49 of rotor 3 in the impact direction and the stiffness of flexible arms 6, 7, 8 of movable part 5 are selected to maintain gear contact between rotor 3 and movable element 5, regardless of the direction and intensity of the impact.

[0067] In a fourth embodiment of the piezoelectric motor, which is similar to all the embodiments described above but not shown in the figures, the impact is electronically detected by the piezoelectric voltage sensed in arms 6, 7, and 8. For example, during operation of motors 1 and 30, one of arms 6, 7, and 8 can temporarily switch from actuator mode to detector mode via a transistor in the detection device. Thus, the detection device periodically detects whether an impact occurs during one-third of the rotation of the gear drive point. Where appropriate, it can perform correction to the next excitation signal, for example by temporarily increasing the amplitude of the applied AC voltage to force contact during and after the impact.

[0068] It should be understood that various modifications and / or improvements and / or combinations that are obvious to those skilled in the art can be made to the different embodiments of the invention disclosed above without departing from the scope of the invention as defined by the appended claims.

Claims

1. A rotary piezoelectric motor, the motor comprising: - A rotor, configured to rotate and actuate mechanical devices. - Stator (2), which is configured to rotate the rotor, the stator (2) includes a piezoelectric actuator, the piezoelectric actuator being provided with a resonator (29) arranged to perform an oscillating motion. The stator (2) is characterized in that the stator (2) includes a fixed element (4) and the resonator includes a movable element (5), the movable element (5) being arranged at a distance from and connected to the fixed element (4), the piezoelectric actuator being configured to move the movable element (5) against the rotor to rotate the rotor, the movement of the movable element (5) causing the rotor to rotate in a first direction, wherein the movable element (5) has an annular shape and the rotor is arranged within the annulus.

2. The piezoelectric motor according to claim 1, wherein, The resonator (29) includes at least one flexible arm that is connected at one end to the fixed element (4) of the stator (2) and at the other end to the movable element (5) of the stator (2).

3. The piezoelectric motor according to claim 1 or 2, wherein, The movable element (5) performs orbital motion in a second direction opposite to the first direction.

4. The piezoelectric motor according to claim 1 or 2, wherein, During motor operation, the movable element (5) is always in contact with the rotor.

5. The piezoelectric motor according to claim 3, wherein, The movement of the movable element (5) causes the rotor to rotate continuously.

6. The piezoelectric motor according to claim 1 or 2, wherein, The contact between the movable element (5) and the rotor is within the ring.

7. The piezoelectric motor according to claim 1 or 2, wherein, The rotor includes a toothed wheel, and the ring includes an internal gear system (10) that engages with the external gear system (12) of the toothed wheel.

8. The piezoelectric motor according to claim 1 or 2, wherein, The movable element (5) cannot rotate or move on its own.

9. The piezoelectric motor according to claim 2, wherein, The flexible arms (6, 7, 8) perform radial reciprocating motion, causing the movable element to swing and move.

10. The piezoelectric motor according to claim 1 or 2, wherein, The movable element (5) is arranged around the rotor.

11. The piezoelectric motor according to claim 1 or 2, wherein, The rotor and / or the stator (2) are obtained by micromachining.

12. The piezoelectric motor of claim 2, comprising means for constantly or temporarily adjusting the mechanical tension of each flexible arm (6, 7, 8) by means of a DC bias voltage or by means of changing the amplitude of an AC voltage.

13. The piezoelectric motor according to claim 2, wherein, The flexible arms (6, 7, 8) are phase-shifted between two continuous arms. The signal is actuated, and N is the number of arms.

14. The piezoelectric motor according to claim 1 or 2, wherein, The resonator (29) oscillates at a frequency corresponding to its inherent frequency.

15. The piezoelectric motor according to claim 1 or 2, wherein, The rotor includes flexible blades (49) for maintaining gear transmission with the movable element (5) in the event of an impact.

16. The piezoelectric motor according to claim 1 or 2, wherein, The piezoelectric motor is used in the timepiece.

17. The piezoelectric motor according to claim 2, wherein, The resonator (29) includes two flexible arms.

18. The piezoelectric motor according to claim 2, wherein, The resonator (29) includes three or four flexible arms.

19. The piezoelectric motor according to claim 17 or 18, wherein, The flexible arms are distributed at an angle around the movable element (5).

20. The piezoelectric motor according to claim 11, wherein, The rotor and / or the stator (2) are made of silicon or metal.

21. A timepiece comprising a watch movement, said watch movement including a gear transmission configured to rotate at least one hand, characterized in that, The timepiece includes a piezoelectric motor according to any one of the preceding claims, the piezoelectric motor being arranged to actuate the gear transmission.

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