The present disclosure relates to energy harvesting apparatus and methods and, more particularly, to an energy harvesting apparatus and method that makes use of a spring disc, commonly known as a “Belleville” spring, to harvest vibration energy from a vibrating structure.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Electrically-powered devices require a power source. Electrical power can be supplied in a variety of ways, including through wiring from a centralized source or from a battery. Many electrical devices are used on mobile platforms, such as aircraft, aerospace vehicles, rotorcraft, etc. The wiring typically used in these applications is heavy and costly. The use of batteries requires periodic replacement and/or recharging. In addition, a battery contains corrosive materials, and this can be a factor in limiting the use of a battery in some applications. Furthermore, in some aerospace and aircraft applications such as flight testing, various forms of sensors are located in areas where it would be costly to route power wiring.
Various attempts have been made to use piezoelectric material as a component of an energy harvesting device. When piezoelectric material is strained, an electrical charge is generated through the coupling of the mechanical and electrical states of the material. The charge generated can be useful electrical energy. The development of areas and methods of harnessing this electrical energy is finding considerable interest at the present time for their potential to power various forms of sensors and electrical components, and especially in applications where it is impractical or difficult to make use of a battery and/or wiring leading to the sensor or device.
Various forms of piezoelectric devices have attempted to convert vibrating energy from a structure into useful electrical energy. However, many piezoelectric energy harvesting devices have difficulty harvesting vibration energy at low frequencies (i.e., frequencies typically less than 100 Hz). The problem with such piezoelectric devices is their lack of sensitivity to low frequency vibration energy. A device able to convert low frequency vibration energy into useful electrical energy would thus prove highly useful in a wide variety of applications where the need exists to power a remotely located sensor or other form of electronic device.
The present disclosure is related to a system and method for harvesting vibration energy. The system and method is particularly useful for harvesting low frequency vibration energy, but is not limited to such, but rather is responsive to a relatively wide frequency range of vibration energy.
In one embodiment a vibration energy harvesting apparatus is provided that includes a first disc spring having an axial center and an outer peripheral area, a second disc spring having an axial center and an outer peripheral area, and an electrically responsive material secured to a surface of the first disc spring. Alternatively, electrically responsive material may be secured to surfaces of both of the disc springs. The disc springs may each comprise what is commonly known as a “Belleville” spring. Alternatively, any like disc having a generally frusto-conical shape with a spring-like quality may potentially be employed.
A support ring may be used for supporting outer peripheral areas of the first and second disc springs and holding the disc springs in facing relationship to one another. When loaded, disc springs exhibit a non-linear stiffness behavior, with regions of low stiffness. A fastening assembly is used to apply a preload force to the disc springs to soften the disc springs to a low stiffness. The apparatus may be supported from a vibrating structure via the support ring or a portion of the fastening assembly. With either mounting arrangement, the disc springs are free to move in response to vibration energy from a vibrating structure.
In one form the electrically responsive material comprises a piezoelectric ring of material that is adhered to an associated one of the spring discs. The piezoelectric material generates electrical signals in response to changes in strain as the disc flexes slightly in response to the vibration energy transmitted to it from the vibrating structure. The electrical signal generated from the piezoelectric material can be used to power an external device or even to actuate some form of actuator, sensor or other electronic or electromechanical component or it can be conditioned and stored in a circuit for later use.
The present disclosure also relates to a method for harvesting vibration energy. In one implementation the method involves securing a pair of spring discs to a vibrating structure, where the spring discs are pre-loaded with a force sufficient to deflect them to a condition of low stiffness, to thus significantly soften the spring discs. This makes the spring discs highly sensitive to low frequency, low amplitude vibration energy.
An electrically responsive material is secured to the spring disc. The material generates an electrical output signal in response to changes in strain that it experiences as the spring disc flexes in response to vibration transmitted to it from the vibrating structure. The electrical output signals from the electrically responsive material may then be used to power or actuate an electrical, electronic or electro-mechanical device.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Referring to
The apparatus 10 generates electrical power in response to the vibration energy from the vibrating structure 12 and transmits the electrical power to a suitable power conditioning system 18, which then supplies an electrical power output 20 to an electronic or electromechanical device requiring electrical power. While the apparatus 10 is especially well suited for providing electrical power to power other electrical, electronic or electromechanical devices, it will be appreciated that the electrical output signals generated by the apparatus 10 could just as readily be used to turn on and off a sensor or other electrical, electronic or electromechanical component or be conditioned and stored in a circuit for later use.
Referring to
The first disc spring 22 further includes a ring of electrically responsive material 32, which in one preferred form may comprise a piezoelectric material ring. Similarly, the second disc spring 24 includes an electrically responsive material ring 34 secured thereto, which also may comprise a piezoelectric material ring. For convenience, material rings 32 and 34 will be referred to as “piezoelectric” material rings throughout the following discussion. It will be appreciated, however, that any material that is able to generate electrical signals in response to changes in strain may be used in place of a piezoelectric material. Such other materials might include polyvinylidine fluoride (PVDF) film. Each piezoelectric material ring 32,34 is further arranged coaxially with the axial center of its associated disc spring 22 or 24.
Electrical conductor 22a is electrically coupled to the piezoelectric material ring 32 by any suitable conductive adhesive or mechanical connection, while electrical conductor 22b may be similarly coupled to the first disc spring 22. Conductors 22a and 22b feed the potential difference signal generated across the piezoelectric material ring 32 to a first input channel of the power conditioning system 18. Conductor 24a is electrically coupled to the second piezoelectric material ring 34 by any suitable conductive adhesive or mechanical connection, and conductor 24b may be similarly conductively coupled to the second disc spring 24. Conductors 24a and 24b feed the potential difference signal generated across the second piezoelectric material ring 34 into a second input second channel of the power conditioning circuit 18. The power output 20 of the power conditioning system 18 represents an electrical signal that may be related to the vibration energy harvested by the apparatus 10.
Referring further to
With further reference to
With further reference to
Nonconductive adhesive 54 is used to provide a strong bond between the piezoelectric material layer 32 and the outer surface 56 of the disc spring 22. Prior to adhering the piezoelectric material layer 32, it is also preferred to thoroughly clean the outer surface 56 of the disc spring 22, and possibly also to sand the surface 56 so that a surface is presented that will enable a strong bond to be achieved. For the conductive adhesive 50, various forms of adhesive may be used, but one suitable adhesive is CHO-BOND®, a two-part conductive epoxy commercially available from Chomerics, a company of the Parker Hannifin Corporation. The non-conductive adhesive 54 may also take a plurality of forms, but one suitable adhesive is commercially available LOCTITE-HYSOL® 9330 two-part epoxy.
Once the adhesives 50 and 54 have cured, any tooling being used to hold the disc springs 22,24 in place during the curing process may be removed. Once this manufacturing operation has been completed for both of the disc springs 22 and 24, the apparatus 10 may be assembled and the nut 42 adjustably tightened on the fastening member 14. The nut 42 is tightened sufficiently to provide a preload force that deflects each of the disc springs 22 and 24 to approximately a midpoint of its low stiffness region. The low stiffness region for one of the disc springs 22 or 24 is defined by arrow 58 in
With further reference to
Still another factor that must be taken into account is the added stiffness of the piezoelectric material rings 32 and 34. Preferably, the added stiffness provided by the piezoelectric material rings 32 and 34 is accounted for by selecting disc springs 22 and 24 that have suitably high height-to-thickness ratios. Generally, the higher the height-to-thickness ratio for the disc spring, the more piezoelectric material that can be attached (i.e., the greater the thickness of the piezoelectric material layer 34 that can be used). It is also possible to use disc springs having tapering wall thicknesses. It will also be appreciated that the threaded fastener 14, the nut 42 and the washer 40 may also impact tuning of the disc springs 22 and 24, and therefore will likely need to be accounted for when setting the preload force for the disc springs 22,24.
Referring briefly to
In operation, as the apparatus 10 of
With the apparatus 10, the opposed arrangement of the disc springs 22 and 24 allows each of the disc springs to be preloaded to its low stiffness region and the deflecting motion of the disc springs is not in anyway impeded by the motion of the other. In certain geometries and/or applications, it may be preferable to provide the support ring 26 with a height that enables each of the disc springs 22 and 24 to flex beyond its flattened position.
An alternative implementation of the apparatus 10 involves securing the apparatus 10 to a vibrating structure by using a portion of the threaded fastening member 14. The fastening member 14 would need to have a length sufficient to allow for this. With this arrangement, the “input” vibration energy would be applied to the fastening member 14, which would then cause flexing of the disc springs 22 and 24. One advantage of this implementation would be that the mass of the support ring 26 (
The disc springs 22 and 24 are able to respond to a wide frequency range of low amplitude vibration energy. The apparatus 10 is responsive to a vibration energy having a frequency as low as about 5 Hz or potentially even lower. This is due in part to the low stiffness of the disc springs 22,24 when they are preloaded. Some forms of vibration energy harvesting devices have relied on biasing a support member to a “buckling” point to soften the biasing member, and thus heighten its responsiveness to vibration energy. However, buckling is highly sensitive to boundary conditions that can sometimes be difficult to closely manage during a manufacturing process. The low stiffness of the disc springs 22 and 24 can be achieved in large part because of their natural force-deflection characteristics, arising from their axisymmetric geometry. This helps to make the disc springs 22 and 24 less sensitive to boundary conditions than devices that employ buckling to soften the support element.
Referring now to
Another arrangement for forming a magnetic bearing is shown in
While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/672,695 filed on Feb. 8, 2007. The entire disclosure of the above application is incorporated herein by reference.
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Number | Date | Country | |
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20100237748 A1 | Sep 2010 | US |
Number | Date | Country | |
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Parent | 11672695 | Feb 2007 | US |
Child | 12792151 | US |