High-performance piezoelectric motor

Abstract

To provide a symmetrical construction of a piezoelectric motor.SOLUTION: A piezoelectric motor 11 comprises: a frame 12 having a first frame side and a second frame side; a first actuator assembly; and a second actuator assembly. The first actuator assembly comprises a first piezoelectric actuator 10a and two rollers 32a, 34a, where each of the rollers 32a, 34a is pressed between the first piezoelectric actuator 10a and the first frame side. The second actuator assembly comprises a second piezoelectric actuator 10b and two rollers 34b, 32b, where each of the rollers 34b, 32b is pressed between the second piezoelectric actuator and the second frame side. The motor further comprises a pre-loaded spring provided between the first actuator assembly and the second actuator assembly to push them against the first frame side and the second frame side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The subject matter of the present disclosure relates to high performance piezoelectric motors. More particularly, the subject matter of the present disclosure relates to symmetrical structures of piezoelectric motors. [Background technology]

[0002] U.S. Patent No. 5,777,423 to Zumeris, entitled "Ceramic Motor," incorporated herein by reference in its entirety, discloses a pair of piezoelectric micromotors for providing motion to a body, including two rectangular piezoelectric plates, each having first and second long sides, first and second short sides, a front and a back surface, electrodes attached to the front and back surfaces, and a ceramic spacer attached to the first long side, the ceramic spacer engaging the surface of the body. The first short side of the first plate is adjacent to and substantially parallel to the first short side of the second plate. A resilient force is applied to a portion of each plate, pressing the ceramic spacer against the surface of the body. A voltage source charges at least some of the electrodes with an excitation voltage.

[0003] U.S. Patent No. 7,183,690 to Shiv et al., entitled "Resonance Shifting," discloses a piezoelectric vibrator having a thin rectangular piezoelectric plate with two short sides and two long sides, and two large flat surfaces in which the plate has a transverse resonant vibration mode parallel to the short sides and a longitudinal resonant vibration mode parallel to the long sides.

[0004] A paper written by Gal Peled, Roman Yasinov, and Nir Karasikov, titled "Performance and Applications of L1B2 Ultrasonic Motors," published in Actuators 2016, 5, 15; doi:10.3390 / act5020015, discloses details of the piezoelectric motor and its operation. Summary of the Invention

[0005] According to a first aspect of the subject matter of the present disclosure, a piezoelectric motor is provided comprising: a frame having a first frame side and a second frame side; a first actuator assembly and a second actuator assembly, wherein the first actuator assembly comprises a first piezoelectric actuator and two rollers, each of the rollers being pressed between the first piezoelectric actuator and the first frame side; and the second actuator assembly comprises a second piezoelectric actuator and two rollers, each of the rollers being pressed between the second piezoelectric actuator and the second frame side; and at least one preload spring provided between the first actuator assembly and the second actuator assembly and pressing the first actuator assembly and the second actuator assembly against the first frame side and the second frame side, respectively.

[0006] In some embodiments, each of the rollers is positioned within an indentation in the corresponding frame side.

[0007] In some embodiments, each of the first actuator assembly and the second actuator assembly further comprises a contact plate affixed to a corresponding piezoelectric actuator such that each of the rollers can rotate between the contact plate and the corresponding frame side.

[0008] In some embodiments, each of the first and second actuator assemblies further includes a cushion member disposed between the contact plate and the corresponding piezoelectric actuator.

[0009] In some embodiments, the frame sides, rollers, and contact plates are made of metal.

[0010] In some embodiments, the roller is cylindrical.

[0011] In some embodiments, the first and second piezoelectric actuators push a load in an X direction, perpendicular to the Y direction defined by the direction of rotation of the roller, and the stiffness of the piezoelectric motor relative to the frame is much higher in the X direction than in the Y direction.

[0012] In some embodiments, the high stiffness of the piezoelectric motor relative to the frame in the X direction is determined by the stiffness of the metal frame, rollers and contact plate.

[0013] In some embodiments, the first piezoelectric actuator and the second piezoelectric actuator are pushed in the Y direction against the load by at least one spring-loaded support, and the low stiffness of the piezoelectric motor relative to the frame in the Y direction is determined by the stiffness of the spring-loaded support.

[0014] Ensuring low stiffness and low losses associated with the motion of the piezoelectric actuator in the Y direction (perpendicular to the direction of motion) while providing high stiffness in the X direction (direction of motion) is another aspect of the subject matter of this disclosure. All this is necessary for a piezoelectric motor to ensure that the piezoelectric material itself is not brittle and is not affected by high structural stiffness.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosed subject matter belongs.Although methods and materials similar or equivalent to those described herein can be used to implement or test the present invention, suitable methods and materials are described below.In the event of conflict, the present specification, including definitions, shall prevail.In addition, materials, methods, and examples are for illustrative purposes only and are not intended to be limiting.

[0016] The features presented above can be used individually or in combination all together. [Brief explanation of the drawings]

[0017] With reference to the accompanying drawings, several embodiments of the disclosed subject matter are described, by way of example only. Referring now specifically to the drawings in detail, it is believed that the details shown are by way of example only and for purposes of illustrative discussion of preferred embodiments of the disclosed subject matter, and are presented in order to provide the most useful and readily understood description of the principles and conceptual aspects of the disclosed subject matter. In this regard, no attempt has been made to show structural details of the disclosed subject matter more than are necessary for a fundamental understanding of the disclosed subject matter, and the description taken together with the drawings will make apparent to those skilled in the art how several forms of the disclosed subject matter may be embodied in practice.

[0018] In the drawings:

[0019] [Figure 1] 1A-1C schematically illustrate a top view of a piezoelectric motor with the cover removed, according to some exemplary embodiments of the disclosed subject matter. [Figure 2A] 2A-2C schematically illustrate some more details of the piezoelectric motor shown in FIG. 1, according to some example embodiments of the disclosed subject matter. [Figure 2B] 2A-2C schematically illustrate some more details of the piezoelectric motor shown in FIG. 1, according to some example embodiments of the disclosed subject matter. [Figure 2C] 1 illustrates a schematic diagram of some components of a piezoelectric motor, according to some example embodiments of the disclosed subject matter. [Figure 3A] 1A and 1B schematically illustrate a front view of a piezoelectric motor assembly comprising a stack of four piezoelectric pair motors, according to some exemplary embodiments of the disclosed subject matter. [Figure 3B] 1A and 1B schematically illustrate a front view of a piezoelectric motor assembly comprising a stack of two piezoelectric pair motors, according to some exemplary embodiments of the disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0020] Before describing at least one embodiment of the disclosed subject matter in detail, it is to be understood that the disclosed subject matter is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments or of being practiced or carried out in various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The drawings are generally not to scale. For clarity, non-essential elements have been omitted from some of the drawings.

[0021] The terms "comprises," "comprising," "includes," "including," and "having," as well as their conjugations, mean "including but not limited to." The term "consisting of" has the same meaning as "including and limited to."

[0022] The term "consisting essentially of" means that a composition, method, or structure may include additional ingredients, steps, and / or components, but only if the additional ingredients, steps, and / or components do not materially alter the basic and novel characteristics of the claimed composition, method, or structure.

[0023] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" can include a plurality of compounds, including mixtures thereof.

[0024] Throughout this application, various embodiments of the presently disclosed subject matter may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed subject matter. Thus, the description of a range should be considered to have specifically disclosed all possible subranges as well as individual numerical values within that range.

[0025] It is understood that certain features of the disclosed subject matter that are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, for brevity, various features of the disclosed subject matter that are described in the context of a single embodiment may also be provided separately or in any suitable subcombination, or as suitable in other described embodiments of the disclosed subject matter. Certain features described in the context of various embodiments should not be considered essential features of those embodiments, unless the embodiment is inoperable without those elements.

[0026] In the discussion of the various figures set forth herein below, like numbers refer to like parts. Specifically, numbers followed by a letter such as "a" or "b" may mark symmetrical elements. To avoid cluttering the text, numbers followed by the letter "x" refer to any character that follows that number in the drawing; for example, 10x can represent either 10a or 10b.

[0027] Reference is now made to Figure 1, which schematically illustrates a top view of a piezoelectric motor with its cover removed, according to some exemplary embodiments of the disclosed subject matter. Piezoelectric motor 11 has a frame 12 that houses two piezoelectric actuators 10a and 10b in a substantially symmetrical configuration. Figure 1 illustrates one major face of, for each actuator, a relatively thin, rectangular piezoelectric ceramic actuator 10x (x represents either a or b) for use in a motor according to preferred embodiments of the present invention.

[0028] Optionally, a medium to high stiffness piezoelectric material with a medium to high quality coefficient is used for the ceramic actuator 10x. This and other optional features provide improved performance, including slightly higher operating frequency per length of the piezoelectric element, a higher mechanical power to weight ratio, and improved efficiency.

[0029] In an exemplary, non-limiting embodiment, four electrodes 14x, 16x, 18x, and 20x are plated or otherwise attached to one side (hereinafter, the "first side") of the piezoelectric ceramic actuator 10x, forming a rectangular checkerboard pattern, each covering substantially one-quarter of the first side. The opposite side (hereinafter, the "second side") of the piezoelectric ceramic is preferably substantially completely covered by a single electrode (not shown). The diagonally arranged electrodes (14x and 20x, 16x and 18x) are electrically connected by wires 22x and 24x. Alternatively, the electrodes can be connected by printed circuit technology. The electrodes on the second side are preferably grounded or floating. A spacer (hard ceramic chip) 26x is attached to a short side 28x of the piezoelectric ceramic actuator 10x, preferably at the center of the short side 28x, for example, by adhesive bonding. Alternatively, the spacer or chip 26x can be part of the piezoelectric ceramic actuator 10x.

[0030] The piezoelectric ceramic actuator 10x has multiple resonances. In particular, the dimensions of the piezoelectric ceramic actuator 10x are selected so that the Dx and Dy resonances are closely spaced and have overlapping excitation curves and an appropriate phase shift (preferably 90 degrees) between them, where Dx and Dy are two-directional X and Y motions indicated by corresponding arrows 1 and 2. In particular, the resonances that can be used in accordance with embodiments of the disclosed subject matter are the one-half (1 / 2) mode resonance L1 for Dy and the one-half (1.5) mode resonance B2 for Dx. However, other resonances can be used depending on the dimensions of the ceramic actuator 10x.

[0031] When the piezoelectric ceramic actuator 10x is excited by a frequency within the resonant band, both the Dx and Dy resonances are excited, preferably at a 90-degree phase shift. This excitation typically causes elliptical motion of the spacer 26x and a force exerted by the spacer 26x on the load or body 30, which is pressed against the spacer 26x by the force of the spring-loaded supports 44x on the element 10x. The surface of the load 30 is shown as straight and can move relative to the external structure 13 by sliding thereon or rolling on load rollers 3 or other types of low-friction, high-stiffness bearings. Alternatively, the surface of the load 30 can be curved, such as the surface of a rotating cylinder or section of a cylinder. Note that the load 30 can be stationary while the motor 11 moves relative to it.

[0032] In this exemplary embodiment, both piezoelectric ceramics 10a and 10b are restrained from movement by two pairs of rollers, 32a and 34a, 32b and 34b, respectively, which are pressed against frame 12 by the force of two spring-loaded supports 36 and 38.

[0033] Rollers 34x and 32x are designed to slide in the Y direction with low friction, while providing high rigidity for movement in both directions of the X axis (-X and +X) while reducing mechanical losses. Preferably, rollers 32x and 34x, as well as the surfaces they roll on, are made of a hard material, such as metal or ceramic, and are smoothly polished. This arrangement may provide better rigidity than using levers or elastic holders. This arrangement may also provide better low losses than using sliding supports or fixed supports (whereas it is difficult to avoid movement in the Y direction at the support points due to the imperfect straightness of 30).

[0034] Preferably, rollers 34x and 32x do not rest directly on the piezoceramic material of actuator 10x. Instead, contact plates 98a and 98b are attached to ceramic material actuators 10a and 10b, respectively, as seen in more detail in Figures 2A-B. Contact plate 98x is optionally a multi-layer plate having a hard, preferably metal, layer that contacts the rollers, and a softer, preferably plastic, layer that acts as a cushion to prevent damage to the brittle ceramic plate 10x.

[0035] The spring-loaded supports 36 and 38 preferably comprise compressed metal springs. Two coil springs may be used, although more than one spring may be used. Other spring configurations, such as leaf springs, may also be used. The use of metal springs may be superior to using elastic materials such as silicone rubber because they may provide better control of force, require looser tolerances, and may also have lower mechanical losses and less outgassing, making them more suitable for high-vacuum applications. These springs provide a constant force greater than the effective force of the motors, thus maintaining rollers 32x and 34x in contact with both the frame 12 and the contact plate; thus, their deformation determines the lateral stiffness in the X direction.

[0036] The spacer 26x is pressed against the load 30 by a spring-loaded return support 44x. The spring-loaded support 44x preferably presses against the center of a second short side 43x of the piezoelectric ceramic actuator 10x, opposite the short side 28x. The return support 44x preload provides pressure between the spacer 26x and the load 30, thereby transferring movement of the spacer 26x to the load 30. Preferably, the spring has a low spring constant so that misalignment of the strip 30 does not affect the motor preload force.

[0037] It should be appreciated that, due to the low spring constant, the spring-loaded return support 44x has a time response that is much slower than the cycle of the frequency at which the piezoelectric ceramic actuator 10x is excited. Thus, the face of the spacer 26x that presses against the load 30 moves slightly to the side away from the load 30 during a portion of the piezo excitation cycle and as the ceramic actuator 10x contracts, shifting its end 28x through 26x to the opposite side of the load 30. During the force-inducing portion of the cycle, as the ceramic actuator 10x expands and its end 28x shifts in the opposite direction, the spacer 26x presses against the body 30, applying motion or force to the load 30. The papers and patents cited in the Background section and incorporated herein by reference provide more details regarding the movement and deformation of ceramic actuators used in piezoelectric motors.

[0038] The spring-loaded return supports 44x preferably comprise compressed metal springs with a low spring constant. Coil springs can be used, but many other spring types can be used. Other spring shapes, such as leaf springs, can be used. The use of metal springs can be superior to using resilient materials such as silicone rubber because they can provide better control of force, and they can also have fewer mechanical losses and lower outgassing, making them more suitable for high-vacuum applications. Springs with a low spring constant are more tolerant of mechanical tolerances for straightness of motion.

[0039] As shown in the figures, the spring-loaded return supports 44x can be placed directly on the frame 12 or can be placed against the return plate 5. The compression of the spring-loaded return supports 44x is optionally adjustable by a mechanical adjustment 6, which can be a screw or other means of adjustment for adjusting the distance between the frame 12 and the return plate 5. A single adjustment can be used. Alternatively, the compression at each return support 44x is optionally adjusted individually by using two adjustments between the frame 12 and the return plate 5. Still alternatively, the compression at each of the return supports 44x is optionally adjusted individually by using a corresponding individual adjustment between the frame 12 and the return plate 5.

[0040] To facilitate transportation of motor 11 and ease its installation, push back plate 7 is optionally placed in front of ceramic actuator 10x. When push back plate 7 is pushed in direction −Y by a retraction mechanism (not seen here), it further compresses support 44x so that the ends of spacers 26x protrude from openings 8 in frame 12 just touching load 30. After motor 11 is installed, push back plate 7 is released (as shown in the figure), allowing spacers 26x to press against load 30. Optionally, push back plate 7 can be reused when motor 11 needs to be released, replaced, or repaired.

[0041] Reference is made to FIG. 2A, which schematically illustrates some more details of a piezoelectric motor, in accordance with some example embodiments of the disclosed subject matter.

[0042] Only elements of Fig. 2A that have not already been described in the text will be considered here. Some elements of the lower half of motor 11 are not marked here to reduce clutter in the figure. This figure shows a schematic top view of motor 11 with the cover removed. Motor 11 comprises two assemblies 93a and 93b in a symmetrical configuration.

[0043] In this figure, the push-back plate 7 is pushed in the direction −Y (Y axis is indicated by the numeral 2) by a retraction mechanism (not seen here) so that the ends of the spacers 26x optionally protrude slightly from the openings 8 in the frame 12 and touch the load 30 (not shown in this figure). Thus, in this retracted position, the spacers 26x protrude with zero force to touch the hard ceramic load 30, allowing for easy installation of the motor 11 in its desired position and removal of the motor 11, for example for service or replacement.

[0044] Shown here is holder 50a, which holds ceramic actuator 10a at holding points 56a, 57a, 58a, and 59a. The locations of holding points 56a, 57a, 58a, and 59a are selected to be at or near the inflection (node) points of the resonance excited in ceramic actuator 10a, where heat generation is significant, so that heat can be removed by conduction from ceramic actuator 10a through holder 50a. Additionally, at the inflection points of the resonance excited in ceramic actuator 10a, movement in the X direction is minimal or zero, so the force and rotational motion of holder 50a relative to rollers 34a and 32a is predominantly or only in the Y direction. Heat can also be dissipated through spacer 26x and by radiation. Because this motor is optionally vacuum compatible (which can be made to avoid the use of lubricants), heat dissipation by air convection may not be available.

[0045] In the illustrated non-limiting example seen in FIG. 2A, the locations of retention points 57x and 59x are typically 0.13L, and the locations of retention points 56x and 58x are typically 0.87L, where L is the length of actuator 10x measured from tip side 51x. In a non-limiting exemplary embodiment, ceramic actuator 10x is approximately 28.8 mm long and 7.7 mm wide. However, other dimensions are possible, providing close proximity to the L1 and B2 resonances.

[0046] An optional damper 55a, placed between the ceramic actuator 10a and the back of the holder 50a, protects the fragile ceramic 10a. The damper 55a is preferably made of a resilient material such as Viton elastomer.

[0047] Optional contact plates 54a and 52a are positioned on holder 50a to provide a hard, smooth surface for rollers 34a and 32a to roll on. Contact plates 54a and 52a can be made of metal, such as steel, aluminum, or a combination, while holder 50a can be made of plastic or metal. This reduces Hertzian stress and improves stiffness in the X direction. Optionally, a damper layer (not seen here) is positioned between the metal contact plates and holder 50a. In some embodiments, contact plates 54a and 52a are combined into a single plate, as seen in FIGS. 1 and 2B. Optional indentations 94x and 92x in frame 12 are provided and each configured to receive rollers 34x and 32x, respectively. Preferably, the indentations have a radius of curvature larger than the radius of the corresponding roller. The indentations align rollers 43x and 34x to their desired positions. Additionally, the curvature of the indentations increases the contact area between the rollers and the frame, thus increasing the stiffness of the structure in the X-direction 1. However, for small movements, such as those experienced during operation of the motor 11, the rollers 34x and 32x are largely free to move between the frame 12 and the contact plates 54x and 52x, allowing for low-friction movement of the ceramic actuator 10x in the Y-direction 2. Preferably, the rollers have a cylindrical shape, which increases stiffness compared to a spherical shape while maintaining a low coefficient of friction. While the indentations can have a cylindrical shape, other concave shapes can be used without limiting the scope of the disclosed subject matter.

[0048] Optionally, a concave shape can be used on contact plates 54x and 52x, or on both contact plates 54x and 52x and frame 12.

[0049] 2B, which schematically illustrates some more details of a piezoelectric motor, according to some example embodiments of the disclosed subject matter. A top view of the motor 11 and its cover is shown.

[0050] Rollers 32x and 34x rest against indentations 92x and 94x, respectively, in frame 12 on one side and against contact plate 98x on the other side.

[0051] Here, roller 32a is partially seen behind roller carriage 97a. The portion of roller 32a that is behind cover 97a is shown in dashed lines. Roller carriage 97x holds the roller to prevent movement in the Z direction, perpendicular to directions X(1) and Y(2).

[0052] Also visible in this view are covers 95a and 95b, respectively, which hold motors 10a and 10b to frame 12 and prevent movement of assembly 93x in the Z direction while allowing the motors to vibrate freely in the XY plane. Cover 95x is secured to frame 12 by wings 91x.

[0053] Reference is made to FIG. 2C, which schematically illustrates some components of a piezoelectric motor, according to some example embodiments of the disclosed subject matter.

[0054] (i) shows rollers 32x and 34x in roller carriage 97a.

[0055] (ii) shows a holder 50x showing a bay 85x for holding a damper 55x.

[0056] (iii) shows the cover 95x showing the wing 91x.

[0057] Reference is made to FIG. 3A, which schematically illustrates a front view of a piezoelectric motor assembly comprising two stacks of four piezoelectric motors, according to some exemplary embodiments of the disclosed subject matter.

[0058] 3A shows a schematic front view of a piezoelectric motor assembly 411 comprising two stacks of four piezoelectric motors 11a-d. The piezoelectric motor assembly is fixed to an electromotive device, for example, by connecting members 60.

[0059] 3B, which schematically illustrates a front view of a piezoelectric motor assembly including two stacks of piezoelectric motors, according to some exemplary embodiments of the disclosed subject matter. Note that piezoelectric motor assemblies including different numbers of piezoelectric motors can optionally be fabricated in other assembly configurations, such as a 2D matrix. For example, a single motor assembly 11x can be used, or a stack of N motor assemblies 11x can be used, where N is an integer. Optionally, the motor assemblies 11x may not be precisely aligned one above the other.

[0060] While the present invention has been described in connection with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims. All publications, patents, and patent applications mentioned in this specification are incorporated herein by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated herein by reference. Furthermore, citation or identification of a reference in this application should not be construed as an admission that such reference is available as prior art to the present invention.

Claims

1. A piezoelectric motor, a frame having a first frame side and a second frame side; a first actuator assembly and a second actuator assembly, the first actuator assembly: a first piezoelectric actuator; two rollers, each configured to be pressed and slide between the first piezoelectric actuator and the first frame side; Equipped with the second actuator assembly: a second piezoelectric actuator; two rollers, each configured to be pressed and slide between the second piezoelectric actuator and the second frame side; Equipped with a first actuator assembly and a second actuator assembly; at least one preloaded compressed metal coil spring provided between the first actuator assembly and the second actuator assembly, urging the first actuator assembly and the second actuator assembly toward the first frame side and the second frame side, respectively; A piezoelectric motor comprising:

2. The piezoelectric motor of claim 1 , wherein each of the rollers is positioned within an indentation in a corresponding frame side.

3. 2. The piezoelectric motor of claim 1, wherein each of the first actuator assembly and the second actuator assembly further comprises a contact plate, the contact plate affixed to a corresponding piezoelectric actuator such that each of the rollers can rotate between the contact plate and its corresponding frame side.

4. The piezoelectric motor of claim 3 , wherein each of the first actuator assembly and the second actuator assembly further comprises a cushion member disposed between the contact plate and the corresponding piezoelectric actuator.

5. The piezoelectric motor of claim 3 , wherein the frame sides, the rollers, and the contact plates are made of metal.

6. The piezoelectric motor of claim 1 , wherein the roller is cylindrical.

7. the first piezoelectric actuator and the second piezoelectric actuator push a load in an X direction perpendicular to a Y direction defined by a direction of rotation of the roller; the stiffness of the piezoelectric motor relative to the frame is much higher in the X direction than in the Y direction; The piezoelectric motor according to claim 1 .

8. The piezoelectric motor of claim 5 , wherein a high stiffness of the piezoelectric motor relative to the frame in the X direction is determined by stiffnesses of the metal frame, the two rollers, and the contact plate.

9. the first piezoelectric actuator and the second piezoelectric actuator are urged in the Y direction against the load by at least one spring-loaded support having a low spring constant; a low stiffness of the piezoelectric motor relative to the frame in the Y direction determined by the stiffness of the spring-loaded support; 8. The piezoelectric motor according to claim 7.

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