Patent Application
20090121587
The present disclosure relates to piezoelectric devices and methods, and more particularly to piezoelectric motors and energy harvesting devices and methods, and more particularly to an energy harvesting apparatus and method that generates a negative spring force to overcome the inherent stiffness in a piezoceramic beam.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Piezoceramic based motors, actuators and energy harvesters are rapidly gaining popularity for diverse applications where either energy harvesting is performed, or where the use of a piezoceramic element is being used to control movement of another element, for example an actuator.
The following United States patents, all owned by the Boeing Company, are directed to piezoelectric technology and/or piezoelectric controlled devices, and all are hereby incorporated by reference into the present disclosure: U.S. Pat. Nos. 6,894,460; 6,858,970; 6,563,250; 6,307,301; 6,265,810; and 6,320,707.
One limitation with bimorph piezoceramic beams employed in energy harvesting and various control applications is the inherent stiffness of the piezoceramic material. This stiffness must be overcome before a piezoceramic beam is able to vibrate. This limitation tends to make a piezoceramic beam less sensitive to small amplitudes of vibration energy, and also tends to limit the displacement of a free end of the beam in response to vibration energy, or in response to an electrical signal applied to the piezoceramic beam.
The present disclosure relates to systems and methods making use of an electrostrictive beam that more efficiently and effectively harvests vibration energy, or alternatively an electrostrictive beam that can be used to produce a relatively large displacement, for driving or controlling an external device, in response to the application of an electrical signal to the beam.
In one embodiment the present disclosure provides an energy harvester system having a piezoelectric beam having opposing first and second ends, with the first end being fixedly supported to a support structure. A negative spring force subsystem is included that has a first end fixedly secured against movement, and a second end secured to the second end of the piezoelectric beam. The negative spring force subsystem including a linkage system and a biasing element operably associated with said linkage system for applying an adjustable negative spring force to the piezoelectric beam to soften the piezoelectric beam.
In one specific embodiment the linkage system includes a rod over which the biasing element, which in this example is formed by a coil spring, is positioned. A linear slide and a tension nut are also disposed on the rod, with the coil spring disposed between the linear slide and the tension nut. A swing arm is pivotally coupled at one end to the linear slide and at the opposite end to a free end of the piezoelectric beam. The tension nut can be adjusted to apply a preload force to the piezoelectric beam, via the coil spring, that causes the beam to bend sufficiently to overcome the inherent stiffness in the piezoelectric beam. When the preload force is properly adjusted, the free end of the piezoelectric beam is able to move between two stable positions in an over center like fashion, in response to very little external vibration energy.
In another embodiment a piezoelectric apparatus is disclosed that makes use of a piezoelectric beam and a negative spring force subsystem for softening the piezoelectric beam to produce movement oscillating motion of the piezoelectric beam between two stable positions. The oscillating motion of the piezoelectric beam is used to drive an external device, for example a linear motor, or alternatively a device requiring a rotational input drive signal.
The present disclosure also includes a method for forming a drive implement responsive to electrical input energy. The method may involve supporting a first end of a piezoelectric beam fixedly from a support structure. A negative spring force is then applied to the piezoelectric beam to flex the beam sufficiently to overcome a stiffness of the beam, and such that a second end of the beam is able to move readily in an over center fashion between two stable positions in response to the application and removal of electrical signals to said piezoelectric beam. The intermittent or oscillating motion of the second end of the piezoelectric beam can then be used drive an external device, for example an actuator or a flight control surface. 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
In this exemplary embodiment the system 10 includes an electrically sensitive (e.g., electrostrictive) beam, for example a bimorph piezoceramic beam 12, and a negative spring force subsystem 14 operatively coupled to the beam 12. The beam 12 has a first end 16 and a second end 18. The first end 16 is fixedly coupled or supported from a base 20 or other support structure so that the first end 16 is held rigidly against movement. The second end 18 is free to move.
The negative spring force subsystem 14 includes a tensioner member in the form of a rod 22. The rod 22 has a first end 24 that is coupled to the base 20 and a second end 26 that is operatively coupled to a linear slide mechanism 28. The rod 22 may be formed by steel, aluminum or any other material that is structurally rigid and resistant to bending. A biasing element, in this example a coil spring 30, is disposed over the second end 26 of the rod and abuts a portion of the linear slide mechanism 28. A tubular tension nut 32 is also positioned over the rod 22 and includes a set screw 34 that enables the tension nut 32 to be secured fixedly on the rod 22 at a desired longitudinal position.
With further reference to
With brief reference to
With brief reference to
Referring again to
In the present exemplary embodiment of the system 10, it has been found that the two stable positions can be created if the bimorph piezoceramic beam 12 is preloaded such that force in the compression spring 30 is given by the following equation:
where “EI” is the bending stiffness of the piezoceramic beam, “Lbeam” is the length of the piezoceramic beam, “Llinkarm” is the length of the link arm and “Θ” is the bend angle of the beam.
Referring further to
Referring now to
In one exemplary implementation shown in
In another exemplary implementation shown in
From the foregoing it will be appreciated that the system 10 is equally well adapted for use as an energy harvesting system, or as a system that can control or drive an external component, or function as an actuator. The increased displacement of the second end 18 of the beam 12, as a result of the negative spring force subsystem 14 being able to overcome the inherent stiffness of the bimorph piezoceramic beam 12, enables both a greater magnitude electrical signal to be generated from oscillating motion of the second end 18 of the beam, when the system 10 is being used for energy harvesting purposes. Still further, a greater displacement of the second end 12 is produced when the system 10 is configured to drive an external component.
Those skilled in the art will recognize modifications or variations that 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.
