LT7007B - Five degrees of freedom piezoelectric drive - Google Patents

Abstract

The invention discloses a high-precision piezoelectric drive which generates independent rotary motion of the spherical rotor about three axes and sliding motion in the plane, and improves the dynamic characteristics and control of the drive. The drive consists of two piezoelectric rings (2, 8) fixed on elastic supports (5, 10) mounted on elastic rings (4, 7), and connected by an elastic cone (6). Three spherical contacts (3, 9) are installed on both piezoelectric rings and are used to rotate the rotor (1) or move the system on a flat hard surface. An asymmetric electric signal is used for excitation. The dynamic characteristics are increased when the resonant frequency of the support coincides with the resonant frequency of the bending vibrations of the ring. The location of the supports corresponds to the vibration nodes of the piezoelectric ring. Control of the rotational and sliding movement of the piezoelectric drive is improved by the use of a cone-shaped stator that allows reducing of the transmission of vibrations from the upper ring to the lower and vice versa.

Description

TECHNICAL FIELD

The invention belongs to the fields of electro-mechanical, mechatronic systems and robotics. It is an actuator designed to create high-precision multi-purpose rotary and sliding motion systems, including reverse, and can be applied to precise sliding and rotary motion positioning systems, such as optical filter, laser beam or optical lens positioning systems, as well as precision positioning of specimens and other objects. systems or devices.

STATE OF THE ART

With the rapid development of precision positioning, optics and microscopy systems, the aim is to increase their resolution and accuracy. In the development of multifunctional precision positioning systems with many degrees of freedom, the problem of reducing the number of actuators and the volume occupied by them and improving and expanding their functionality is faced. The application of classical electromagnetic actuators in multi-functional multi-degree-of-freedom positioning systems is limited due to the design features related to the fact that the actuator's electromagnetic actuator creates a single-degree-of-freedom motion, which complicates the integration of actuators in multi-functional multi-degree-of-freedom positioning systems. One of the research directions is related to the development of multifunctional piezoelectric actuators and actuators with many degrees of freedom, in which the rotary and/or sliding movements of the drive chain or the entire positioning system are not created by the electromagnetic principle, but by transforming electrical energy into high-frequency mechanical vibrations that ensure the drive chain or the sliding and/or rotary movements of the entire positioning system. By controlling the modes and amplitudes of the mechanical vibrations of the actuator, it is possible to achieve multi-degree-of-freedom motions of the drive chain or the entire positioning system with nanometer resolution. This makes it possible to simplify the design of the drive, reduce the dimensions of mechatronic systems, increase the functionality of devices and create integrated mechatronic positioning systems.

A piezoelectric actuator is known, described in patent CN204505286U, which provides the ability to create two degrees of freedom rotary motion. The actuator consists of a cylindrical piezoelectric actuator with two groups of piezoelectric rings.

A sphere-shaped rotor is placed on the upper surface of the cylindrical actuator, which is connected to a ring-shaped structure that generates the rotary movement of the rotor around the axis of symmetry of the actuator. The operating principle of the drive is based on the excitation of bending oscillations of the cylindrical actuator stator by affecting different groups of piezoelectric rings with two harmonic signals with a phase difference of π/2. Stator oscillations generate rotational movements of the rotor using frictional force, which is regulated using a spring of variable stiffness mounted in the lower part of the gear. Considering the design of the drive and the principle of operation, it can be said that the resolution of the rotary motion will directly depend on the friction force and the amplitudes of the electric signals used to excite the drive, thus achieving a flexible control of the resolution of the motions. On the other hand, the design of the drive is complex, the volume it occupies is quite large, so the integration of such a drive into low-volume positioning systems becomes difficult and complicated.

Patent CN106877734B describes a piezoelectric actuator that is used to achieve six-degree-of-freedom sliding-rotational motions of a flat platform. The actuator consists of four identical piezoelectric transducers connected in one cross-shaped structure, and the driving part is placed on the upper part of the cross-shaped structure. The structure itself is anchored immovably in the central lower part of the cross shape. Piezoelectric transducers consist of a cylindrical rod, two groups of piezoelectric rings whose electrodes are divided horizontally and vertically, and a cylindrical counterweight. The operating principle of the actuator is based on the first two perpendicular modes of bending vibrations of a cylindrical rod, the excitation of which is obtained by affecting two groups of piezoelectric rings with two harmonic signals with a phase difference of π/2. In order to obtain the sliding-rotating movements of the flat platform, different excitation schemes of piezoelectric transducers and their excitation sequence are applied. For example, to obtain a sliding movement of the platform in the Y direction, two piezoelectric transducers opposite each other are synchronously excited, and to obtain a rotary movement of the platform around the Z axis, two piezoelectric transducers located on the sides are synchronously excited. Considering the design of the actuator, it can be argued that the integration of the actuator into low-volume, high-precision systems is limited due to the limited ability to scale the actuator. Also, the actuator design is composed of four different piezoelectric transducers, which affects the complex motion resolution control and control, resulting in the need for a complex control and feedback system.

Patent CN109861580B describes a six-degree-of-freedom piezoelectric actuator that can provide rotational and sliding motions of a spherical rotor and a flat platform. A piezoelectric actuator consists of two parts responsible for creating rotary and sliding motions, until these parts are elastically connected to each other to form the overall structure of the actuator. The part of the drive, which is responsible for the rotational movements of the sphere-shaped rotor, consists of piezoelectric rings, the upper electrodes of which are divided into four equal parts, and the rings are assembled into one multilayer package. A spherical rotor is placed on the upper surface of the piezoelectric ring package.

In order to obtain rotary movements of a spherical rotor, two opposite electrodes are affected by saw-tooth signals with a phase difference of π, thus exciting the asymmetric bending oscillations of the multilayer package, which, upon contact with the sphere, are transformed into directional rotary movements of the spherical rotor, the axis of rotation of which is perpendicular to the bending vibration direction of the multilayer package. In order to obtain rotary movements of the rotor in other directions, different pairs of electrodes are excited. The part of the drive that generates the sliding motion consists of piezoelectric rings, the upper electrodes of which are divided into four equal parts, while the rings themselves are assembled into a multilayer piezoelectric package, and on the lower surface of this package, a cone-shaped concentrator is installed, the pointed part of which rests on a flat platform . In order to obtain the sliding motions of the platform, two opposite electrodes are excited by two saw-tooth electrical signals with a phase difference of π. In this way, bending vibrations of the package and the cone-shaped concentrator are excited and a directional sliding motion of the flat platform is obtained, which is generated by applying the inertial principle. The direction of movement of the platform coincides with the line connecting the centers of the stimulated electrodes. In order to obtain bending vibrations of the cone-shaped concentrator in different directions, different pairs of electrodes are excited. Considering the design and operation principle of the actuator, it can be said that the design is complex and has limited scalability, so its application in small-volume positioning systems is limited. Also, the construction of the mounting and load clamping mechanism of this gear is complicated, which limits the application possibilities of this gear.

ESSENCE OF THE INVENTION

The purpose of the invention is to increase the accuracy of the piezoelectric actuator and the dynamic characteristics of the actuator and to improve the control of the movement direction.

The purpose of the invention is achieved by the fact that in a piezoelectric actuator consisting of a cone-shaped elastic hollow stator, consisting of a hollow elastic cone and elastic rings placed at its ends, made of the same material as the hollow cone, and whose inner diameter is equal to the diameters of the cone base and apex, respectively . On the upper surface of both rings, elastic supports are installed, which are integral parts of the cone-shaped stator. There are three supports each in the upper and lower part of the stator, which are arranged every 120°. The position of the supports in the upper and lower part is offset by 60°. Piezoelectric rings of different sizes, whose electrodes are divided into three equal parts, are permanently attached to the supports. On the upper and lower piezoelectric rings at the outer and inner diameters of these rings, three sphere-shaped contact elements are installed every 120°, the difference in position between the contact elements of the upper and lower surface is 60°. A spherical rotor is slidably placed on the upper sphere-shaped contacts, and the contact elements located on the lower ring are slidably placed on a hard flat surface, which allow generating the sliding movement of the gear. By stimulating the corresponding electrode of the piezoelectric rings with non-symmetrical electrical signals, mechanical vibrations of the stator are generated in the contact zone, which are transformed during frictional contact into high-precision rotor rotation or sliding displacement of the drive itself.

In order to improve the control of the rotary and sliding movement of the piezoelectric actuator, the stator has a cone shape and is made of an elastic material, which results in different stiffness of the upper and lower parts, which allows to reduce the transmission of vibrations from the upper elastic ring to the lower contact elements when the upper piezoelectric ring is excited and vice versa. The stiffness differences of the cone-shaped stator, upper and lower parts are selected so that the wide part of the cone-shaped stator corresponds to the outer diameter of the upper piezoelectric ring, and the diameter of the lower cone part corresponds to the inner diameter of the lower ring and has a mutual ratio of 2 or more, and the cone-shaped stator, including elastic after heating, the height is chosen so that the mechanical vibration frequencies of the stator do not coincide with the mechanical vibrations of the upper and lower piezoelectric rings.

The vibration transmission of the piezoelectric ring is reduced by the use of elastic support elements to which the said ring is attached, because the length and thickness of the support elements are selected so that their bending resonant frequency coincides with the resonant frequency of the piezoelectric ring. The performance of the piezoelectric actuator, the rotational speed of the rotor and the speed of the sliding movement of the actuator are increased when the geometric dimensions of the supports are selected so that their resonant frequency corresponding to the first bending vibration mode coincides with the resonant frequency of the bending vibration of the piezoelectric ring attached to the supports, and the mounting locations of the supports match 60° angular difference is maintained between the piezoelectric ring vibration assembly and between the upper and lower support attachment points.

DESCRIPTION OF DRAWINGS

The figures in the drawings are provided as an indication of the possible implementation of the invention and are not intended to limit the scope of the invention. None of the drawings and graphs presented should be considered as limiting, but only as examples of possible embodiments of the invention.

Fig. 1 a,b Five-degree-of-freedom piezoelectric actuator:

(a) isometric view of a five-degree-of-freedom piezoelectric actuator;

(b) - expanded five-degree-of-freedom piezoelectric actuator;

Fig. 2 Five-degree-of-freedom piezoelectric actuator excitation scheme;

Fig. 3 Five-degree-of-freedom piezoelectric actuator vibration modes used to obtain sliding-rotational motion;

(a) - vibration mode used to obtain the rotary motion of the spherical rotor;

(b) is the mode of oscillation used to obtain the sliding motion of the actuator;

DRAWINGS - description of marked objects

- sphere-shaped rotor;

- upper piezoelectric ring;

- sphere-shaped contacts are installed in the inner diameter of the upper ring;

- upper elastic ring;

- upper supports;

- elastic cone;

- lower elastic ring;

- lower piezoelectric ring;

- sphere-shaped contacts are installed in the outer diameter of the lower ring;

- lower supports;

- electrical signal generator;

,13 - commutators of electric excitation signals;

- polarization direction of the lower ring;

- polarization direction of the upper ring;

- upper electrode;

- lower electrode;

- piezoelectric actuator.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the sliding-rotating five-degree-of-freedom piezoelectric actuator is described with reference to the drawings, but the technical implementation of the piezoelectric actuator is not limited to the presented method. Various modifications and improvements to the implementation method are possible.

Detailed description of the drive. The piezoelectric five-degree-of-freedom actuator (18) consists of a stator consisting of an upper elastic ring (4), an elastic cone (6) and a lower elastic ring (7), which are permanently connected to each other. In the free planes of the elastic rings (4,7), the upper and lower supports (5,10) are permanently placed, arranged every 120°, and the angular difference between the arrangement of the upper and lower supports is 60°. The upper and lower piezoelectric rings (2,8), whose upper and lower electrodes (16, 17) are divided into three equal parts, and the polarization vectors (14,15) of the upper and lower ring are directed to the supports (5,10) are elastically mounted in the direction of the ring thickness and is in the opposite direction. In the inner diameter of the upper piezoelectric ring (2), three spherical contacts (3) are elastically installed every 120°, on which the spherical rotor (1) is slidably placed. The angular difference between the upper supports (5) and the upper contacts (3) is 60°. In the outer diameter of the lower piezoelectric ring (8), three sphere-shaped contacts (9) are elastically installed, which are placed every 120°, and the lower contacts (9) and the lower supports (10) the angular difference between them is 60°.

Description of the operation of the piezoelectric actuator. The rotational motion of the spherical rotor (1) is obtained when an asymmetric electrical signal with a frequency f1 equal to the upper piezoelectric ring's frequency f1 is supplied to one third of the upper electrode (16) of the upper piezoelectric ring (2) from the signal generator (11) through the signal commutator (12) (2) the third mode of bending vibrations, as a result of which the corresponding upper spherical contact (3) transmits asymmetric mechanical vibrations of the upper piezoelectric ring (2) to the spherical rotor (1) through the friction force, which are transformed into the rotational movement of the spherical rotor (1), whose axis of rotation is perpendicular to the non-symmetrical mechanical vibrations of the corresponding upper spherical contact (3). In order to obtain the rotation of the sphere-shaped rotor (1) in three different directions, an asymmetric electrical signal from the signal generator (11) is fed through the signal commutator (12) to a selected one third part of the upper electrode (16), thanks to which asymmetric mechanical oscillations perpendicular to the intended sphere are created for the axis of rotation of the shaped rotor (1). By switching the excitation signal between the electrodes in this way, a rotary motion of the rotor with three degrees of freedom is obtained.

In order to reduce the transmission of vibrations of the upper piezoelectric ring (2) to the stator and the lower piezoelectric ring (8), the geometric dimensions of the upper supports (5) are selected so that their first resonant frequency of bending vibrations coincides with the third resonant frequency of bending vibrations of the upper piezoelectric ring (2) f2, which does not coincide with the frequency f1.

The sliding movement of the entire drive (18), including the spherical rotor (1), in the plane is obtained when an asymmetric electrical signal is supplied to one third of the lower electrode (17) of the lower piezoelectric ring (8) from the signal generator (11) through the signal commutator (13) , the frequency of which coincides with the second mode of bending deformations of the lower piezoelectric ring (8), as a result of which the corresponding lower spherical contact (9) transmits asymmetric mechanical vibrations of the lower piezoelectric ring (8) to a hard, flat surface through the frictional force so that the inert principle creates a directional sliding motion of the entire structure, the direction vector of which is parallel to the direction of the inharmonic mechanical vibrations of the lower sphere-shaped contact (9). In order to reduce the transmission of vibrations of the lower piezoelectric ring (8) to the stator and the upper piezoelectric ring (2), the geometric dimensions of the lower supports (10) are selected so that their first resonant frequency of bending vibrations coincides with the second resonant frequency of bending vibrations of the lower piezoelectric ring (8) . In order to obtain sliding movements of the gear (18) in different directions in the plane, an asymmetric signal is supplied from the signal generator (11) through the signal commutator (13) to the selected one third part of the lower electrode (17), thanks to which oscillations parallel to the intended displacement of the gear (18) will be created direction. .

Claims (4)

Piezoelectric actuator (18), consisting of an elastic stator, two piezoelectric rings (2, 8) glued to the stator, a spherical rotor (1) differs in that the stator consists of an elastic cone (6) and two elastic rings (4, 7 ), which are permanently connected to each other and elastic supports (5, 10), on which two piezoelectric rings are attached The drive according to claim 1, which differs in that the geometrical dimensions of the upper and lower supports (5,10) are selected so that the resonant frequency of their bending vibrations coincides with the resonant frequency of the piezoelectric rings (2,8) used to obtain the sliding gear (18) or rotary movements of the sphere-shaped rotor (1). The drive according to claim 1, with the difference that the rotary and sliding movements of the rotor are obtained by separately exciting the upper or lower piezoelectric rings (4, 8) with an asymmetric electric signal of different frequency. The drive according to claim 1, but differs in that the locations of the upper and lower supports (5,10) on the elastic rings (4,7) are selected to coincide with the nodes of the bending vibration mode of the elastic rings, and the difference in the position of the supports between the upper and lower surface elements is 60 degrees.