US20070263887A1

US20070263887A1 - Vibration amplification system for piezoelectric actuators and devices using the same

Info

Publication number: US20070263887A1
Application number: US11/747,516
Authority: US
Inventors: Edward Tanner
Original assignee: Adaptivenergy LLC
Current assignee: Adaptivenergy LLC
Priority date: 2006-05-15
Filing date: 2007-05-11
Publication date: 2007-11-15
Also published as: US20070267940A1; WO2007136593A2; WO2007136593A3; WO2007136594A3; US20070273248A1; US7608984B2; WO2007136594A2; WO2007136595A2; WO2007136595A3

Abstract

A motion amplification apparatus taking the form of a reverse vibration absorber (RVA) comprises a piezoelectric diaphragm (22); a driving diaphragm (26) configured to serve as a driving member for an actuated device (34); a mass (28) attached to the driving diaphragm (26); and, a resilient member (30) configured to connect the piezoelectric diaphragm (22) and the driving diaphragm (26) whereby motion of the piezoelectric diaphragm (22) resulting from application of the drive signal is amplified for driving the actuated device (34). The piezoelectric diaphragm (22) has a drive signal applied thereto and is held stationary around at least a portion of its periphery. The driving diaphragm (26) is also held stationary around at least a portion of its periphery.

Description

This application claims the benefit and priority of the following United States provisional patent applications, all of which are incorporated herein by reference in their entirety: U.S. Provisional Patent application 60/747,286, entitled “COMPRESSOR AND COMPRESSION USING MOTION AMPLIFICATION”; U.S. Provisional Patent application 60/747,287, entitled “MOTION AMPLIFICATION USING PIEZOELECTRIC ELEMENT”; and U.S. Provisional Patent application 60/747,289, entitled “VIBRATION AMPLIFICATION SYSTEM FOR PIEZOELECTRIC ACTUATORS AND DEVICES USING THE SAME”. This application is related to the following simultaneously-filed US patent applications, both of which are incorporated herein by reference: U.S. patent application Ser. No. 11/747,450, entitled “COMPRESSOR AND COMPRESSION USING MOTION AMPLIFICATION” and U.S. patent application Ser. No. 11/747,469, entitled “MOTION AMPLIFICATION USING PIEZOELECTRIC ELEMENT”.

BACKGROUND

1. Field of the Invention
The present invention pertains to amplification of motion such as vibration motion, and particularly to amplification of motion caused by a piezoelectric diaphragm or the like.
2. Related Art and Other Considerations
Piezoelectric diaphragms have been employed in various types of pumps and actuators. As is well known, a piezoelectric material is polarized and will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the piezoelectric effect. Conversely, an applied electric field can cause a piezoelectric material to change dimensions.
There has been considerable interest in using piezoelectric actuators in many applications, but the relatively small displacement produced by a typical piezoelectric actuator is too small to be useful in some applications. While a particular type of piezoelectric device known as a ruggedized laminated piezoelectric or RLP™ provides a considerable displacement improvement over other commercially available piezoelectric actuators, amplifying the displacement even further allows the use of such piezoelectric elements in applications that are not usually considered as candidates for piezoelectric actuation. Among those are miniature gas compressors which require a fairly large diaphragm displacement to operate properly. These compressors are used in many applications, among those being gas sampling and fuel cell balance of plant components. To date the form factor of miniature compressors has been less than desirable. In many applications a much thinner form factor is desired. Furthermore, the current commercially available miniature compressors consume a considerable amount of power thus limiting their applicability in battery powered devices.
Traditionally a vibration absorber is used to minimize the vibration of an object. This is accomplished by attaching a spring-mass system of a known fundamental frequency to the vibrating object. When properly designed, the added spring-mass system provides a force to the vibrating object that is equal in magnitude, but opposite in direction, to the force creating the vibration in the object. The net effect is to eliminate the vibration of the object. In actual practice the complete elimination of the vibration is not achieved, but a properly design vibration absorber can significantly reduce the amplitude of the vibration.

BRIEF SUMMARY

A motion amplification apparatus taking the form of a reverse vibration absorber (RVA) comprises a piezoelectric diaphragm; a driving diaphragm configured to serve as a driving member for an actuated device; a mass attached to the driving diaphragm; and, a resilient member configured to connect the piezoelectric diaphragm and the driving diaphragm whereby motion of the piezoelectric diaphragm resulting from application of the drive signal is amplified for driving the actuated device. The piezoelectric diaphragm has a drive signal applied thereto and is held stationary around at least a portion of its periphery. The driving diaphragm is also held stationary around at least a portion of its periphery.
The apparatus can also (optionally) comprise comprising a mass attached to the piezoelectric diaphragm. In an example implementation, the mass attached to the piezoelectric diaphragm can be centrally attached to a side of the piezoelectric diaphragm which is oriented toward the driving diaphragm. In such implementation, the resilient member is configured to have a first end connected to the mass attached to the piezoelectric diaphragm and a second end connected to the mass attached to the driving diaphragm.
In an example embodiment, the mass attached to the driving diaphragm is centrally attached to a side of the driving diaphragm which is oriented toward the piezoelectric diaphragm. In an example implementation, the driving diaphragm comprises a corrugation near its periphery.
In an example embodiment, each of the following are chosen so that a natural frequency of the motion amplification apparatus is equivalent to a desired driving frequency for the actuated device: a spring constant representing stiffness of the driving diaphragm; a spring constant exerted by a load upon which the driving diaphragm acts; a spring constant of the resilient member; and, the mass attached to the driving diaphragm.
In an example embodiment, the actuated device is a fluid compressor. In another example embodiment, the driving diaphragm contacts or actuates a working element of the actuated device.
A driver (e.g., driving circuit, controller, or processor) is connected to supply the drive signal to the piezoelectric diaphragm. In an example implementation, the driver comprises a resonance detector configured to adjust a drive frequency to maintain system resonance.
The resilient member can take various forms. In one example embodiment, the resilient member is a coil spring. In another example embodiment, the resilient member is a disc spring. In yet another example embodiment, the resilient member comprises one or more leaf springs.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
FIG. 1 is a partial cross-section, partial schematic view of a reverse vibration absorber (RVA) in conjunction with a generic actuated device.
FIG. 2 is a mechanical schematic view of the reverse vibration absorber (RVA) and the generic actuated device of FIG. 1.
FIG. 3 is a cross-section view of a reverse vibration absorber (RVA) in conjunction with a actuated device which takes the form of a compressor.
FIG. 4 is a cross-section view of a reverse vibration absorber (RVA) in conjunction with a actuated device which takes the form of a piston or shaft-driven device.
FIG. 5 is a graph showing displacement amplification achieved by an example embodiment of a reverse vibration absorber (RVA).

DETAILED DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. That is, those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
A vibration absorber in accordance with the technology herein disclosed is essentially operated in reverse to amplify the motion of a piezoelectric actuator. A goal of operation of the reverse vibration absorber (RVA) is not to eliminate the vibration, but to use the vibration absorber to amplify the relatively small amplitude vibrations of a piezoelectric actuator, such as a ruggedized laminated piezoelectric or RLP™.
FIG. 1 shows a non-limiting example embodiment of reverse vibration absorber (RVA) 20. The reverse vibration absorber (RVA) 20 comprises a piezoelectric diaphragm or other piezoelectric element 22; (optionally) a first mass 24 attached to the piezoelectric diaphragm 22; an actuator diaphragm 26 (also known as driving diaphragm 26); a second mass 28 attached to the driving diaphragm 26; and, a resilient member 30 for connecting piezoelectric diaphragm 22 and driving diaphragm 26. The driving diaphragm 26 serves as a driving member for an actuated device 34. In FIG. 1, reverse vibration absorber (RVA) 20 is shown in cross-section, but actuated device 34 is shown generically as a functional block. The actuated device 34 is shown as a functional block in FIG. 1 since actuated device 34 can take diverse forms, and the interface of reverse vibration absorber (RVA) 20 to actuated device 34 can differ according to the form of actuated device 34.
The piezoelectric diaphragm 22 can take various geometrical forms and shapes, but preferably is circular. Whatever form it takes, piezoelectric diaphragm 22 has its periphery grounded, e.g., held in place. Grounding the piezoelectric diaphragm 22 in this way enables the piezoelectric diaphragm 22 to serve as the exciter for reverse vibration absorber (RVA) 20, rather than relying on inertia. In the embodiment shown in FIG. 1, the periphery or circumference of piezoelectric diaphragm 22 is held in place by its attachment to a housing 36. The piezoelectric diaphragm 22 is connected by electrical leads 38 or the like to a driver 40 (e.g., a driver circuit or processor) which supplies a driving signal to piezoelectric diaphragm 22.
The first mass 24 is preferably (but not necessarily) centrally attached to the underside of piezoelectric diaphragm 22.
Similarly the driving diaphragm 26 is also grounded, e.g., by its connection or attachment to housing 36. The second mass 28 is preferably (but not necessarily) centrally carried on a topside of driving diaphragm 26. In the illustrated example embodiment, near its periphery or edge the driving diaphragm 26 has corrugations 42 which provide an additional resilient component to driving diaphragm 26.
The resilient member 30 has a first end connected to piezoelectric diaphragm 22 and a second end connected to driving diaphragm 26. In the embodiment in which one or both of piezoelectric diaphragm 22 and driving diaphragm 26 carry their respective first mass 24 and second mass 28, the first end of resilient member 30 can be connected to the piezoelectric diaphragm 22 via first mass 24 and the second end of resilient member 30 can be connected to driving diaphragm 26 via second mass 28, as shown in FIG. 1.
FIG. 1 also shows that actuated device 34, which typically comprises a load upon which the driving diaphragm 26 acts, can exert a spring constant k_a. In fact, FIG. 2 provides a mechanical schematic of the reverse vibration absorber (RVA) 20 of FIG. 1. The system of FIG. 2 comprises a set of masses that are attached to the piezoelectric diaphragm 22 and the driving diaphragm 26 of the actuated device 34. In some embodiments it is likely that mass m₁would be unnecessary, but it is shown as it may be useful in come applications to more effectively tune the system. Spring k_drepresents the stiffness of the driving diaphragm 26 and spring k_arepresents the stiffness of the load. The core of the system is the mass attached to the driving diaphragm 26, m₂, and the driven spring k_crealized by resilient member 30. These components comprise reverse vibration absorber (RVA) 20.
If the displacement of the mass m₁is denoted X₁and the displacement of mass m₂is denoted X₂then the amplitude of the steady-state response can be written as in Equation 1 and Equation 2. $\begin{matrix} Equation 1 : \\ X_{1} = \frac{(k_{a} + k_{c} + k_{d} - m_{2} ω_{dr}^{2}) F_{0}}{(k_{c} - m_{1} ω_{dr}^{2}) (k_{a} + k_{c} + k_{d} - m_{2} ω_{dr}^{2}) - k_{c}^{2}} \\ Equation 2 : \\ X_{2} = \frac{k_{c} F_{0}}{(k_{c} - m_{1} ω_{dr}^{2}) (k_{a} + k_{c} + k_{d} - m_{2} ω_{dr}^{2}) - k_{c}^{2}} \end{matrix}$
In the foregoing Equations, the force generated by the piezoelectric diaphragm 22 is given by Equation 3.
F _d =F ₀sin ω_dr t Equation 3
As in a classic vibration absorber the steady-state amplitude X₁will be minimized (theoretically it would be zero) provided the numerator of Equation 1 is equal to zero. Simultaneously the steady-state amplitude X₂of the absorber mass m₂, which is attached to the compressor diaphragm, will be maximized. Setting the numerator of Equation 1 equal to zero leads to Equation 4.
k _a +k _c +k _d −m ₂ω_dr ²=0 Equation 4
Rearranging Equation 4 leads to Equation 5. $\begin{matrix} Equation 5 : \\ ω_{dr} = \sqrt{\frac{k_{a} + k_{c} + k_{d}}{m_{2}}} \end{matrix}$
Choosing the values of these three springs and the mass m₂such that the natural frequency of the system is equivalent to the desired driving frequency will maximize the motion of the driving diaphragm 26 and thus the performance of the actuated device 34. Note that this is just the equation describing the natural frequency of a simple single-degree-of-freedom oscillator, where the stiffness of the “spring” is the sum of the stiffness of the load, the stiffness of the driving spring 30, and the stiffness of the driving diaphragm 26.
Example utilizations of the reverse vibration absorber (RVA) include as a mechanical actuator and as or with a fluid compressor. FIG. 3 illustrates an example embodiment in which actuated device 34(3) is a compressor, e.g., a gas compressor. In the compressor 34(3) of FIG. 3 the driving diaphragm 26 acts as a compressor diaphragm upon fluid in a pumping or compression chamber 50. The compression chamber 50 is partially defined by driving diaphragm 26, and partially defined by the housing 36. The housing 36 further has an inlet port 52 and an outlet port 54 through which fluid is respectively admitted and discharged from compression chamber 50. The inlet port 52 can be provided with an inlet valve 56; the outlet port 54 can be provided with an outlet valve 58. In the compressor 34(3), the fluid in the compression chamber 50 is included as a factor in the spring constant k_a.
For a compressor 34(3) the amplification of the piezoelectric vibration is necessary as gases are highly compressible and thus a compressor designed to pump a gas requires the amplitude of the pumping diaphragm to be fairly large. This approach is equally viable for liquid pumps as well as more traditional actuator applications.
FIG. 4 shows use of reverse vibration absorber (RVA) 20 with an actuated device wherein the driving diaphragm 26 serves to contact or actuate an unillustrated working element of the actuated device 34(4). In the embodiment of FIG. 4, driving diaphragm 26 has a piston or actuator shaft 60 attached or secured to its underside and positioned to be an active element for contacting or actuating a responsive mechanism of the actuated device 34(4). The piston or actuator shaft 60 is shown merely to be representative of various types of working members or configurations that can be attached to driving diaphragm 26. The attachment to driving diaphragm 26 can be by any suitable mechanism or technique, such as via adhesive, fastener, or integral formation, for example.
FIG. 5 shows the displacement amplification benefits of the reverse vibration absorber (RVA) 20. In this simulation the peak-to-peak displacement of the mobile stations (MS) 22 is assumed to be 5 mils (0.005 in.). This displacement is amplified by the reverse vibration absorber (RVA) 20 to produce a displacement of the driving diaphragm 26 of 98 mils (0.098 in.) peak-to-peak, for an increase of approximately 20× the displacement of the piezoelectric diaphragm 22. It is anticipated that this displacement amplification factor can be increased through further optimization of the design.
Since backpressure by the actuated device 34, e.g., by the fluid in a compressor used as actuated device 34, increases the effective stiffness of the spring k_a, which in turn will shift the system resonant frequency, the driver 40 for the could be designed with a resonance detection feature that would automatically adjust the drive frequency to maintain system resonance. Driving of to maintain system resonance is explained in simultaneously-filed U.S. Provisional Patent application 60/747,286, entitled “COMPRESSOR AND COMPRESSION USING MOTION AMPLIFICATION”, which us incorporated herein by reference in its entirety. Such driving has the advantage of always producing the maximum flow for a given input and the highest electrical efficiency.
In other embodiments the reverse vibration absorber (RVA) 20 need not necessarily use a coil drive spring for resilient member 30 as shown in FIG. 1. Having a coil spring tends to necessitate a rather tall device to accommodate the coil spring. In some applications a more attractive approach in terms of form factor involves using a disk spring in place of the coil drive spring, thereby providing a far thinner actuator system.
As mentioned above there are many potential applications for this technology. Essentially any application that would benefit from the advantages of piezoelectric actuation, such as low power consumption, small form factor, infinitely variable actuation, etc., would benefit from this technology. Examples include miniature gas compressors, liquid pumps, linear actuators, piezoelectric energy harvesting, etc. The device would be particularly attractive in battery powered applications where available power is limited due to the inherent efficiency of resonant operation.
One exemplary piezoelectric diaphragm which can serve as piezoelectric diaphragm 22 is known as a ruggedized laminated piezoelectric or RLP™, has a central piezoelectric wafer which is laminated to a stainless steel substrate and preferably also has an aluminum cover laminated thereover. Examples of such RLP™ elements, and in some instances pumps employing the same, are illustrated and described in one or more of the following: PCT Patent Application PCT/US01/28947, filed 14 Sep. 2001; U.S. patent application Ser. No. 10/380,547, filed Mar. 17, 2003, entitled “Piezoelectric Actuator and Pump Using Same”; U.S. patent application Ser. No. 10/380,589, filed Mar. 17, 2003, entitled “Piezoelectric Actuator and Pump Using Same”, and U.S. patent application Ser. No. 11/279,647 filed Apr. 13, 2006, entitled “PIEZOELECTRIC DIAPHRAGM ASSEMBLY WITH CONDUCTORS ON FLEXIBLE FILM”, all of which are incorporated herein by reference.
Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”

Claims

1. A motion amplification apparatus comprising:

a piezoelectric diaphragm to which a drive signal is applied and which is held stationary around at least a portion of its periphery;

a driving diaphragm configured to serve as a driving member for an actuated device, the driving diaphragm being held stationary around at least a portion of its periphery;

a mass attached to the driving diaphragm;

a resilient member configured to connect the piezoelectric diaphragm and the driving diaphragm whereby motion of the piezoelectric diaphragm resulting from application of the drive signal is amplified for driving the actuated device.

2. The apparatus of claim 1, further comprising a mass attached to the piezoelectric diaphragm.

3. The apparatus of claim 2, wherein the mass attached to the piezoelectric diaphragm is centrally attached to a side of the piezoelectric diaphragm which is oriented toward the driving diaphragm.

4. The apparatus of claim 1, wherein the resilient member is configured to have a first end connected to the mass attached to the piezoelectric diaphragm and a second end connected to the mass attached to the driving diaphragm.

5. The apparatus of claim 1, wherein the mass attached to the driving diaphragm is centrally attached to a side of the driving diaphragm which is oriented toward the piezoelectric diaphragm.

6. The apparatus of claim 1, wherein the driving diaphragm comprises a corrugation near its periphery.

7. The apparatus of claim 1, wherein each of the following are chosen so that a natural frequency of the motion amplification apparatus is equivalent to a desired driving frequency for the actuated device:

a spring constant representing stiffness of the driving diaphragm;

a spring constant exerted by a load upon which the driving diaphragm acts;

a spring constant of the resilient member;

the mass attached to the driving diaphragm.

8. The apparatus of claim 1, wherein the actuated device is a fluid compressor.

9. The apparatus of claim 1, wherein the driving diaphragm contacts or actuates a working element of the actuated device.

10. The apparatus of claim 1, further comprising a driver connected to supply the drive signal to the piezoelectric diaphragm.

11. The apparatus of claim 1, wherein the driver comprises a resonance detector configured to adjust a drive frequency to maintain system resonance.

12. The apparatus of claim 1, wherein the resilient member is a coil spring.

13. The apparatus of claim 1, wherein the resilient member is a disc spring.

14. The apparatus of claim 1, wherein the resilient member comprises one or more leaf springs.