Piezoelectric motor with bending travelling wave

Abstract

The invention relates to a piezoelectric motor with bending travelling wave, comprising a rotary shaft (4) connected to a rotor (3), a piezoelectric element (2) attached to a vibrating stator (1), and a decoupling web (5) for attaching the vibrating stator to a mounting (7). The mounting (7) is mechanically connected to a base (9) by means of at least one deformable element (10) and at least one piezoelectric actuator (11), so that the support can be deformed angularly relative to the base in order to rotate the shaft when the vibrating stator is no longer electrically powered. The motor is particularly suitable for applications that require micrometre or nanometre accuracies, for example in positioning tools in industrial processes, precise medical robotics or optical applications.

Claims

1. A bending traveling wave piezoelectric motor comprising: a base; a support; a piezoelectric element; a vibrating stator; a rotor; a rotary drive axis; and a decoupling web for fixing of the vibrating stator to the support, wherein the support is mechanically connected to the base via a deformable element and a first piezoelectric actuator, such that the support can be angularly displaced relative to the base to rotate the rotary drive axis when the vibrating stator is no longer supplied by electricity.

2. The bending traveling wave piezoelectric motor according to claim 1, further comprising: a second piezoelectric actuator configured to operate in flexion, mechanically connecting the support to the base, wherein the first piezoelectric actuator is configured to operate in compression.

3. The bending traveling wave piezoelectric motor according to claim 1, wherein the first piezoelectric actuator is configured as a stack.

4. The bending traveling wave piezoelectric motor according to claim 1, further comprising: a piezoelectric mechanical amplification arrangement configured to increase an angular displacement of the support relative to the base.

5. The bending traveling wave piezoelectric motor according to claim 1, wherein the piezoelectric actuator includes a displacement sensor.

6. The bending traveling wave piezoelectric motor according to claim 4, wherein the piezoelectric mechanical amplification arrangement includes a displacement sensor.

7. The bending traveling wave piezoelectric motor according to claim 6, wherein the displacement sensor is used to measure a resisting torque of the bending traveling wave piezoelectric motor during operation.

8. The bending traveling wave piezoelectric motor according to claim 1, wherein the rotary drive axis is hollow.

9. The bending traveling wave piezoelectric motor according to claim 1, further comprising: an electronic supply and control device with two stages including a first stage dedicated to the bending traveling wave piezoelectric motor and a second stage dedicated to the first piezoelectric actuator.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: Example of piezoelectric motor of the state of the art reduced to the three main elements of the motor (exploded view).

(2) FIG. 2: Piezoelectric motor of the state of the art inserted into a support (exploded view).

(3) FIG. 3: First variant of a basic structure of a motor according to the invention (top view).

(4) FIG. 4: Isometric view of the structure of FIG. 3.

(5) FIG. 5: Second variant of a basic structure of a motor according to the invention (top view).

(6) FIG. 6: Isometric view of the structure of FIG. 5.

(7) FIG. 7: Third variant of a basic structure of a motor according to the invention (top view).

(8) FIG. 8: Isometric view of the structure of FIG. 7.

(9) FIG. 9: Example of construction of a motor according to the invention.

NUMERIC REFERENCES USED IN THE FIGURES

(10) 1 Vibrating stator 2 Piezoelectric element 3 Rotor 4 Rotary shaft 5 Decoupling web 6 Printed circuit 7 Support 8 Torque sensor 9 Base 10 Deformable element 11 Piezoelectric actuator 12 Mechanical amplification arrangement 13 Connection wire 14 Cap

(11) The piezoelectric motor of the state of the art illustrated in FIG. 1 is similar to that which is disclosed in the patent U.S. Pat. No. 4,562,374.

(12) The piezoelectric electric element 2 is fixed to the vibrating stator 1. The rotor 3 is pressed mechanically onto the vibrating stator 1 by an axial force (not represented). The vibrating stator 1 comprises a fixing zone, called “decoupling web” 5, which is sufficiently rigid in rotation but sufficiently flexible axially not to disrupt the bending mode generated in the vibrating stator 1. The designation “decoupling web” well illustrates the function of this element which makes it possible to “statically” fix the vibrating stator 1 but which does not disrupt its dynamic behavior at resonance. The rotary shaft 4 is linked mechanically to the rotor 3 such that, upon the rotation thereof, the shaft 4 is set in motion with no mechanical play. In some configurations, the shaft 4 can be a hollow shaft, to allow the passage of wires or light beams for example. The piezoelectric element 2 is generally annular but can, in other embodiments, be composed of several piezoelectric ceramics suitably positioned.

(13) The piezoelectric motor of the state of the art illustrated in FIG. 2 is fixed onto a support 7 positioned in a housing base 9. The support 7 is fixed to the housing 9 via deformable elements 10, of which at least one is provided with a torque sensor 8.

(14) The motor also comprises a printed circuit 6 whose function is to electrically power the motor and process the signals from the various sensors incorporated in the housing (not illustrated).

(15) It should be noted that, when the motor is stopped (without power supply), the main elements of the motor 1-4 are completely secured because they are linked in rotation by the axial force and the resultant friction force. For the rotor 3 and its shaft 4 to have a relative movement with respect to the vibrating stator 1, it is necessary to overcome the holding torque (greater than the maximum torque of the motor).

(16) The first variant basic structure of the motor according to the invention (see FIG. 3) comprises a piezoelectric actuator 11, a support 7, two deformable elements 10, all being positioned inside the base 9 of a housing (not illustrated).

(17) The piezoelectric motor according to the invention, in its variant of FIG. 3, comprises a piezoelectric actuator 11 of “stack” type. The basic structure of the motor comprises two deformable elements 10, positioned such that the longitudinal force exerted by the piezoelectric actuator 11 is translated into an angular displacement of the support 7. The angular displacement of the support 7 has the effect of setting the assembly consisting of the vibrating stator 1, the rotor 3 and the shaft 4 in rotational motion. More specifically, the vibrating stator 1 is fixed mechanically to the support 7 by means of the decoupling web 5. When the motor is stopped, the friction force between the rotor 3 and the vibrating stator 1 secure the shaft 4 and the support 7 in rotation.

(18) FIG. 4 shows the mechanical links between the components 7, 9, 10, 11 which form the basic structure of the motor.

(19) The structure illustrated in FIG. 5 two piezoelectric actuators 11 positioned symmetrically on each side of the support 7.

(20) When one of the piezoelectric actuators 11 is deformed by traction, the other piezoelectric actuator 11 is deformed by compression. The deformation force of the support 7 is ensured by the piezoelectric actuator 11 which works by compression. The structure of FIG. 5 shows an example of deformable element 10. Obviously, any other deformable element geometry that makes it possible to obtain a similar effect can be used, namely ensuring a rotational deformation of the support 7 while maintaining a high degree of mechanical rigidity in rotation. In particular, and without being exhaustive, the piezoelectric actuators 11 can be positioned perfectly symmetrically with respect to the plane in which the deformable elements 10 are situated in order for the torque of the motor (in the direction of rotation) to always exert a compression force in one or other of the piezoelectric actuators 11.

(21) FIG. 6 shows the mechanical links between the components 7, 9, 10, 11 which form the basic structure of the motor.

(22) In the variant structure of FIG. 7, the actuators are positioned and fixed inside mechanical amplification arrangements 12, commonly called “flextensors”, which have the effect of augmenting the angle of rotation of the support 7. This amplification mechanism is known but the present invention also includes any other type of mechanical amplification mechanism, more particularly those that use “pivot” points and elastic deformations.

(23) FIG. 8 shows the mechanical links between the components 7, 9, 10, 11, 12 which form the basic structure of the motor.

(24) The variant of FIG. 8 shows electrodes and the connection wires 13 that make it possible to electrically power the piezoelectric actuators 11. In the nanometric or micrometric positioning applications, it is necessary to be able to control these displacements by sensors. Several techniques are known to the person skilled in the art, in particular the extensiometry gauges positioned either directly on the “stack” (and measuring the elongation of the actuator) or in combination with a deformation element as defined, for example by the deformable elements (and measuring the deformation of these elements). It should be noted that the same deformation sensors that make it possible to control the high-resolution angular displacements due to the piezoelectric actuators can be used to measure the resisting torque of the motor. By using either the control electronics of the traveling wave piezoelectric motor, or the control electronics of the piezoelectric actuators, the field of application of the sensors can be dissociated while exploiting the same output values. Other types of sensors able to measure very small deformations or displacements can be implemented according to the state of the art and in accordance with the knowledge of the person skilled in the art. Capacitive, piezoresistive, optical or Hall-effect sensors can notably be used.

(25) Finally, FIG. 9 presents a piezoelectric motor according to the invention, associated with the structure illustrated in FIGS. 7 and 8.

(26) The base 9 of the housing and the cap 14 make it possible to exert the axial force necessary to press the rotor 3 onto the vibrating stator 1. This axial force is relayed by a ball bearing (not represented). The angular movement induced by the piezoelectric actuators 11 drives all of the basic structure of the motor and the shaft 4. The motor according to the invention preferably comprises a two-level power supply and control electronic circuit board (not represented). The first level consists of the electronic elements that make it possible to generate the electric power supply signals of the traveling wave motor, in particular two electrical waves lying between 20 and 60 kHz, phase-shifted by π/2, and with a voltage of between 20 and 200 V, depending on the characteristics of the motors. When the motor is stopped, the second level has electronic components whose role is to supply DC (or low-frequency) current to the piezoelectric actuators appropriately.

(27) As indicated previously, the motor according to the present invention entails the use of at least one piezoelectric actuator 11 operating either by compression or by traction (sufficient condition). An actuator of bimetallic strip type operating by bending can be implemented. This type of actuator is characterized by greater displacement, which facilitates the mechanical integration but the forces are much lower. In the micrometric positioning applications, it is important to maintain a high degree of rigidity in rotation. That is why the actuators of “stack” type will be preferred in this field of use. Being much more rigid, they are capable of generating significant forces but, on the other hand, low displacements of the order of 50 to 100 μm of travel. The piezoelectric actuator of “stack” type 11 has the advantage of maintaining on the support 7 a high degree of rigidity in rotation. Such an actuator can be driven by DC (positive or negative) voltages of a few volts which makes the power supply electronics much more simple. However, this type of actuator is sensitive to the tensile stress leading the “stack” to break or be damaged. To mitigate this effect, the “stack” should be mechanically prestressed or be made to operate only by compression. For that reason, and for other reasons linked to the symmetry of the mode of actuation of the actuators with respect to the axis of rotation, it is advantageous to have two piezoelectric actuators 11 to rotationally deform the support 7.

(28) If it is wanted to increase the angular travel in the displacement of the support 7, it is sufficient to amplify the displacement of the piezoelectric actuator or actuators 11.

(29) The piezoelectric motor according to the invention can advantageously be used for very diverse micropositioning operations, in relation for example to optronics components, manipulators with force feedback (haptic interface), robotic arms for any industrial or medical application, high-precision process tooling (semiconductors), hexapods, active vibration control, fluid minipumps, solenoid valves, actuators compatible with applications in a vacuum, in high magnetic fields or for controlling optical paths.

(30) It goes without saying that the invention is not limited to the examples illustrated.