US20060021261A1 - Footwear incorporating piezoelectric energy harvesting system - Google Patents

Footwear incorporating piezoelectric energy harvesting system Download PDF

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US20060021261A1
US20060021261A1 US11/184,588 US18458805A US2006021261A1 US 20060021261 A1 US20060021261 A1 US 20060021261A1 US 18458805 A US18458805 A US 18458805A US 2006021261 A1 US2006021261 A1 US 2006021261A1
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transducer
piezoelectric
layer
plucker
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Bradbury Face
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Face Bradbury R
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    • AHUMAN NECESSITIES
    • A43FOOTWEAR
    • A43BCHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B13/00Soles; Sole and heel units
    • AHUMAN NECESSITIES
    • A43FOOTWEAR
    • A43BCHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B3/00Footwear characterised by the shape or the use
    • AHUMAN NECESSITIES
    • A43FOOTWEAR
    • A43BCHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B3/00Footwear characterised by the shape or the use
    • A43B3/0005Footwear provided with electrical or electronic systems
    • AHUMAN NECESSITIES
    • A43FOOTWEAR
    • A43BCHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B3/00Footwear characterised by the shape or the use
    • A43B3/0005Footwear provided with electrical or electronic systems
    • A43B3/0015Footwear provided with generator
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02NELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N2/00Electric machines in general using piezo-electric effect, electrostriction or magnetostriction
    • H02N2/18Electric machines in general using piezo-electric effect, electrostriction or magnetostriction producing electrical output from mechanical input, e.g. generators

Abstract

An article of footwear having a piezoelectric energy harvesting apparatus in the sole member. Walking or running applies a first force deforming a piezoelectric actuator, thereby generating electrical energy. An energy storage circuit stores electrical energy generated by the piezoelectric actuator for later application to electrical devices.

Description

  • This application claims the benefit of priority from earlier filed provisional patent application 60/589,087 filed Jul. 19, 2004.
  • BACKGROUND OF THE INVENTION
  • 1. Field of Invention
  • The present invention relates to an energy harvesting system incorporated in footwear. More specifically the present invention relates to footwear incorporating at least one piezoelectric element which, when activated, enables the wearer of the footwear to harvest energy from the deformation of the piezoelectric element.
  • 2. Description of the Prior Art
  • The present invention is a unique article of footwear which incorporates a piezoelectric system which may be advantageously used in a preferred embodiment of the invention to enable the wearer of said article of footwear to store energy harvested from the piezoelectric element. Energy generated by a piezoelectric element as a result of the impact of the footwear against the ground is stored in an energy storage circuit and is later released at an advantageous time.
  • The prior art includes devices which emit light when the footwear impacts or departs from the ground. Lighted footwear seen in the prior art typically comprises one or more sources of electric light, a small portable power source, such as a dry-cell battery, and electrical circuitry to connect the power source to the light sources electrically, which circuitry usually includes sensing means for sensing the desirable dynamic forces and switching the light sources on and off in a desirable fashion.
  • In U.S. Pat. No. 45,188,447, L. Chiang, et al., describe a lighted footwear system in which the lights are actuated by the impact of the footwear against an object, such as the ground. In this prior system, a piezoelectric crystal operates as a voltage generator to generate a brief voltage pulse, the amplitude of which is related to the amount of inertial force incident upon the crystal. The voltage pulse is used as the input of the battery-driven amplifier, which, in turn, drives the lights, such that the intensity of the single pulse of light emitted by the lights is related to the amount of force with which the footwear impacts the object. The Chiang, et al. device and other prior lighted footwear devices create a lighted effect that is novel and pleasing to the eye, but does not store the energy for later use in any way.
  • Accordingly, an inertially responsive article of footwear which is actuated by impact of the footwear against the ground and which incorporates a piezoelectric element capable of sustaining high loads is highly desirable.
  • SUMMARY OF THE INVENTION
  • In view of the foregoing disadvantages in the prior art, the present invention provides an article of footwear which stores energy generated by a piezoelectric element as a result of the impact of the footwear against the ground. The footwear comprises a piezoelectric element in the sole of the footwear, which generates electrical energy when deformed by the impact of the footwear against an object, such as the ground. The electrical energy is stored in energy harvesting and storage circuitry for use at a later time.
  • Accordingly, it is an object of the present invention to provide a device of the character described which stores the energy generated by the piezoelectric element upon impact of the footwear against the ground.
  • It is a further object of the present invention to provide a device of the character described in which a piezoelectric element is deformed by the impact of the footwear against the ground.
  • It is a further object of the present invention to provide a device of the character described in which the voltage potential created by the deformation of the piezoelectric element is stored in energy storage circuitry for use at a later time.
  • It is another object of the present invention to provide a device of the character described which is inexpensive and of a simple and uncluttered design.
  • Further objects and advantages of this invention will become apparent from a consideration of the drawings and ensuing description thereof.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is an elevation view showing the details of construction of a flextensional piezoelectric transducer used in the present invention, as an electroactive generator;
  • FIG. 1 a is an elevation view showing the details of construction of the flextensional piezoelectric generator of FIG. 1 having an additional prestress layer;
  • FIG. 2 is an elevation view showing the details of construction of an alternate multi-layer flextensional piezoelectric generator used in a modification of the present invention;
  • FIG. 2 a is an elevation view showing the details of construction of the flextensional piezoelectric generator of FIG. 1 a with a flat rather than arcuate profile;
  • FIG. 3 is a side elevation with a shoe in phantom showing a piezoelectric energy harvesting system constructed in accordance with the present invention;
  • FIG. 4 is a side elevation of the piezoelectric energy harvesting system shown in FIG. 3 with a first force being applied to the piezoelectric element, i.e. by bending the shoe by walking;
  • FIG. 5 is a side elevation with a shoe in phantom showing another embodiment of a piezoelectric energy harvesting system constructed in accordance with the present invention;
  • FIG. 6 is a side elevation of the piezoelectric energy harvesting system shown in FIG. 5 with a first force being applied to the piezoelectric element, i.e. by bending the shoe by walking;
  • FIG. 7 is a side elevation with a shoe in phantom showing yet another embodiment of a piezoelectric energy harvesting system constructed in accordance with the present invention;
  • FIG. 8 is a side elevation of the piezoelectric energy harvesting system shown in FIG. 7 with a first force being applied to the piezoelectric element, i.e. by deflecting a plucker assembly by walking;
  • FIGS. 9 a-b are elevations of the plucker assembly in FIGS. 7-8 showing the plucker and actuator in the undeflected and deflected position;
  • FIG. 9 c is a plan view of the plucker assembly in FIGS. 9 a-b;
  • FIGS. 10 a-e are detailed elevations of a plucker assembly and actuator edge in the various stages of deflection;
  • FIGS. 11 a-e are detailed elevations of an alternate “double” plucker assembly and actuator edge in the various stages of deflection;
  • FIGS. 12 a-c show the electrical signal generated by the transducer of FIG. 10, the electrical output signal of the rectifier at the junction with the capacitor and the regulated electrical signal respectively;
  • FIGS. 12 d-f show the electrical signal generated by the transducer of FIG. 11 when plucked twice, i.e., sequentially, the electrical output signal of the rectifier at the junction with the capacitor and the regulated electrical signal respectively;
  • FIG. 13 is a schematic of the components of a circuit for an energy harvesting system in the shoes of FIGS. 3-8;
  • FIG. 14 is a schematic of an exemplary circuit used as an energy harvesting system in the shoes of FIGS. 3-8; and
  • FIG. 15 is a schematic of another exemplary circuit used as an energy harvesting system in the shoes of FIGS. 3-8.
  • DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • As seen in FIG. 3, modern footwear, particularly the type of athletic and casual shoes to which the present invention is readily adapted, typically comprise a soft, flexible upper portion 28 adapted to surround at least a portion of the upper surface of a wearer's foot, and a resilient sole portion 26 attached to the bottom of the upper portion 28 and adapted to underlie the wearer's foot and protect it against uncomfortable contact with the ground.
  • Typical materials for the upper portion 28 include leather and man-made sheet materials, such as polyvinyl or polyurethane sheets, or combinations of these, which are die- or laser-cut and then stitched together over a foot-shaped cast to form the finished upper 28. The sole portion 26 is typically molded of man-made elastomeric materials, such as rubber, foamed or solid polyurethane or ethylene vinyl acetate, to include certain common structural features, such as a top, or “footbed,” surface 33, a peripheral sidewall surface 30, and may further comprise a series of layered components, such as an outsole component, a midsole component, and an insole component (not illustrated). The sole portion 26 is attached on its upper surface 32 to a lower margin of the upper portion 28, typically by adhesive means.
  • As shown in FIG. 3, a piezoelectric energy harvesting system 24 is advantageously disposed in or molded into a cavity 40 located in the sole portion 26, such that when the contact surface 34 of the sole portion 26 impacts the ground 44 the piezoelectric energy harvesting system 24 is actuated. It should be understood that the piezoelectric energy harvesting system 24 is mounted in the sole portion 26 substantially near the contact surface 34, such that the energy transferred to the piezoelectric energy harvesting system 24 by the impact of the contact surface 34 with the ground 44 is maximized, and attenuation of said energy in the section 36 of the sole portion 26 between the ground 44 and the piezoelectric energy harvesting system 24 is minimized. The piezoelectric harvesting system is preferably located in a rear portion, or heel portion, of the sole portion, but may advantageously be located anywhere in the sole portion such as the front or central portions which are subject to deflective forces that may be transferred to the piezoelectric energy harvesting system.
  • Electroactive Generator
  • Piezoelectric and electrostrictive materials (generally called “electroactive” devices herein) develop an electric field when placed under stress or strain. The electric field developed by a piezoelectric or electrostrictive material is a function of the applied force and displacement causing the mechanical stress or strain. Conversely, electroactive devices undergo dimensional changes in an applied electric field. The dimensional change (i.e., expansion or contraction) of an electroactive element is a function of the applied electric field. Electroactive devices are commonly used as drivers, or “actuators” due to their propensity to deform under such electric fields. These electroactive devices when used as transducers or generators also have varying capacities to generate an electric field in response to a deformation caused by an applied force. In such cases they behave as electrical generators.
  • Electroactive devices include direct and indirect mode actuators, which typically make use of a change in the dimensions of the material to achieve a displacement, but in the present invention are preferably used as electromechanical generators. Direct mode actuators typically include a piezoelectric or electrostrictive ceramic plate (or stack of plates) sandwiched between a pair of electrodes formed on its major surfaces. The devices generally have a sufficiently large piezoelectric and/or electrostrictive coefficient to produce the desired strain in the ceramic plate. However, direct mode actuators suffer from the disadvantage of only being able to achieve a very small displacement (strain), which is, at best, only a few tenths of a percent. Conversely, direct mode generator-actuators require application of a high amount of force to piezoelectrically generate a pulsed momentary electrical signal of sufficient magnitude to activate a latching relay.
  • Indirect mode actuators are known to exhibit greater displacement and strain than is achievable with direct mode actuators by achieving strain amplification via external structures. An example of an indirect mode actuator is a flextensional transducer. Flextensional transducers are composite structures composed of a piezoelectric ceramic element and a metallic shell, stressed plastic, fiberglass, or similar structures. The actuator movement of conventional flextensional devices commonly occurs as a result of expansion in the piezoelectric material which mechanically couples to an amplified contraction of the device in the transverse direction. In operation, they can exhibit several orders of magnitude greater strain and displacement than can be produced by direct mode actuators.
  • The magnitude of achievable deflection (transverse bending) of indirect mode actuators can be increased by constructing them either as “unimorph” or “bimorph” flextensional actuators. A typical unimorph is a concave structure composed of a single piezoelectric element externally bonded to a flexible metal foil, and which results in axial buckling (deflection normal to the plane of the electroactive element) when electrically energized. Common unimorphs can exhibit transverse bending as high as 10%, i.e., a deflection normal to the plane of the element equal to 10% of the length of the actuator. A conventional bimorph device includes an intermediate flexible metal foil sandwiched between two piezoelectric elements. Electrodes are bonded to each of the major surfaces of the ceramic elements and the metal foil is bonded to the inner two electrodes. Bimorphs exhibit more displacement than comparable unimorphs because under the applied voltage, one ceramic element will contract while the other expands. Bimorphs can exhibit transverse bending of up to 20% of the bimorph length.
  • For certain applications, asymmetrically stress biased electroactive devices have been proposed in order to increase the transverse bending of the electroactive generator, and therefore increase the electrical output in the electroactive material. In such devices, (which include, for example, “Rainbow” actuators (as disclosed in U.S. Pat. No. 5,471,721), and other flextensional actuators) the asymmetric stress biasing produces a curved structure, typically having two major surfaces, one of which is concave and the other which is convex.
  • Thus, various constructions of flextensional piezoelectric and ferroelectric generators may be used including: indirect mode actuators (such as “moonies” and, CYMBAL); bending actuators (such as unimorph, bimorph, multimorph or monomorph devices); prestressed actuators (such as “THUNDER” and rainbow” actuators as disclosed in U.S. Pat. No. 5,471,721); and multilayer actuators such as stacked actuators; and polymer piezofilms such as PVDF. Many other electromechanical devices exist and are contemplated to function similarly to generate power for harvesting in the invention.
  • Referring to FIG. 1: The electroactive generator preferably comprises a prestressed unimorph device called “THUNDER”, which has improved displacement and load capabilities, as disclosed in U.S. Pat. No. 5,632,841. THUNDER (which is an acronym for THin layer composite UNimorph ferroelectric Driver and sEnsoR), is a unimorph device in which a pre-stress layer is bonded to a thin piezoelectric ceramic wafer at high temperature. During the cooling down of the composite structure, asymmetrical stress biases the ceramic wafer due to the difference in thermal contraction rates of the pre-stress layer and the ceramic layer. A THUNDER element comprises a piezoelectric ceramic layer bonded with an adhesive (preferably an imide) to a metal (preferably stainless steel) substrate. The substrate, ceramic and adhesive are heated until the adhesive melts and they are subsequently cooled. During cooling as the adhesive solidifies the adhesive and substrate thermally contracts more than the ceramic, which compressively stresses the ceramic. Using a single substrate, or two substrates with differing thermal and mechanical characteristics, the actuator assumes its normally arcuate shape. The transducer or electroactive generator may also be normally flat rather than arcuate, by applying equal amounts of prestress to each side of the piezoelectric element, as dictated by the thermal and mechanical characteristics of the substrates bonded to each face of the piezo-element.
  • The THUNDER element 12 is as a composite structure, the construction of which is illustrated in FIG. 1. Each THUNDER element 12 is constructed with an electroactive member preferably comprising a piezoelectric ceramic layer 67 of PZT which is electroplated 65 and 65 a on its two opposing faces. A pre-stress layer 64, preferably comprising spring steel, stainless steel, beryllium alloy, aluminum or other flexible substrate (such as metal, fiberglass, carbon fiber, KEVLAR™, composites or plastic), is adhered to the electroplated 65 surface on one side of the ceramic layer 67 by a first adhesive layer 66. In the simplest embodiment, the adhesive layer 66 acts as a prestress layer. The first adhesive layer 66 is preferably LaRC™-SI material, as developed by NASA-Langley Research Center and disclosed in U.S. Pat. No. 5,639,850. A second adhesive layer 66 a, also preferably comprising LaRC-SI material, is adhered to the opposite side of the ceramic layer 67. During manufacture of the THUNDER element 12 the ceramic layer 67, the adhesive layer(s) 66 and 66 a and the pre-stress layer 64 are simultaneously heated to a temperature above the melting point of the adhesive material. In practice the various layers composing the THUNDER element (namely the ceramic layer 67, the adhesive layers 66 and 66 a and the pre-stress layer 64) are typically placed inside of an autoclave, heated platen press or a convection oven as a composite structure, and slowly heated under pressure by convection until all the layers of the structure reach a temperature which is above the melting point of the adhesive 66 material but below the Curie temperature of the ceramic layer 67. Because the composite structure is typically convectively heated at a slow rate, all of the layers tend to be at approximately the same temperature. In any event, because an adhesive layer 66 is typically located between two other layers (i.e. between the ceramic layer 67 and the pre-stress layer 64), the ceramic layer 67 and the pre-stress layer 64 are usually very close to the same temperature and are at least as hot as the adhesive layers 66 and 66 a during the heating step of the process. The THUNDER element 12 is then allowed to cool.
  • During the cooling step of the process (i.e. after the adhesive layers 66 and 66 a have re-solidified) the ceramic layer 67 becomes compressively stressed by the adhesive layers 66 and 66 a and pre-stress layer 64 due to the higher coefficient of thermal contraction of the materials of the adhesive layers 66 and 66 a and the pre-stress layer 64 than for the material of the ceramic layer 67. Also, due to the greater thermal contraction of the laminate materials (e.g. the first pre-stress layer 64 and the first adhesive layer 66) on one side of the ceramic layer 67 relative to the thermal contraction of the laminate material(s) (e.g. the second adhesive layer 66 a) on the other side of the ceramic layer 67, the ceramic layer deforms in an arcuate shape having a normally convex face 12 a and a normally concave face 12 c, as illustrated in FIGS. 1 and 2.
  • Referring to FIG. 1 a: One or more additional pre-stressing layer(s) may be similarly adhered to either or both sides of the ceramic layer 67 in order, for example, to increase the stress in the ceramic layer 67 or to strengthen the THUNDER element 12B. In a preferred embodiment of the invention, a second prestress layer 68 is placed on the concave face 12 a of the THUNDER element 12B having the second adhesive layer 66 a and is similarly heated and cooled. Preferably the second prestress layer 68 comprises a layer of conductive metal. More preferably the second prestress layer 68 comprises a thin foil (relatively thinner than the first prestress layer 64) comprising aluminum or other conductive metal. During the cooling step of the process (i.e. after the adhesive layers 66 and 66 a have re-solidified) the ceramic layer 67 similarly becomes compressively stressed by the adhesive layers 66 and 66 a and pre-stress layers 64 and 68 due to the higher coefficient of thermal contraction of the materials of the adhesive layers 66 and 66 a and the pre-stress layers 64 and 68 than for the material of the ceramic layer 67. Also, due to the greater thermal contraction of the laminate materials (e.g. the first pre-stress layer 64 and the first adhesive layer 66) on one side of the ceramic layer 67 relative to the thermal contraction of the laminate material(s) (e.g. the second adhesive layer 66 a and the second prestress layer 68) on the other side of the ceramic layer 67, the ceramic layer 67 deforms into an arcuate shape having a normally convex face 12 a and a normally concave face 12 c, as illustrated in FIG. 1 a.
  • Alternately, the second prestress layer 68 may comprise the same material as is used in the first prestress layer 64, or a material with substantially the same mechanical strain characteristics. Using two prestress layers 64, 68 having similar mechanical strain characteristics ensures that, upon cooling, the thermal contraction of the laminate materials (e.g. the first pre-stress layer 64 and the first adhesive layer 66, ) on one side of the ceramic layer 67 is substantially equal to the thermal contraction of the laminate materials (e.g. the second adhesive layer 66 a and the second prestress layer 68) on the other side of the ceramic layer 67, and the ceramic layer 67 and the transducer 12 remain substantially flat, but still under a compressive stress.
  • Alternatively, the substrate comprising a separate prestress layer 64 may be eliminated and the adhesive layers 66 and 66 a alone or in conjunction may apply the prestress to the ceramic layer 67. Alternatively, only the prestress layer(s) 64 and 68 and the adhesive layer(s) 66 and 66 a may be heated and bonded to a ceramic layer 67, while the ceramic layer 67 is at a lower temperature, in order to induce greater compressive stress into the ceramic layer 67 when cooling the transducer 12.
  • Referring now to FIG. 2: Yet another alternate THUNDER generator element 12D includes a composite piezoelectric ceramic layer 69 that comprises multiple thin layers 69 a and 69 b of PZT which are bonded to each other or cofired together. In the mechanically bonded embodiment of FIG. 2, two layers 69 a and 69 b, or more (not shown) may be used in this composite structure 12D. Each layer 69 a and 69 b comprises a thin layer of piezoelectric material, with a thickness preferably on the order of about 1 mil. Each thin layer 69 a and 69 b is electroplated 65 and 65 a, and 65 b and 65 c on each major face respectively. The individual layers 69 a and 69 b are then bonded to each other with an adhesive layer 66 b, using an adhesive such as LaRC-SI. Alternatively, and most preferably, the thin layers 69 a and 69 b may be bonded to each other by cofiring the thin sheets of piezoelectric material together. As few as two layers 69 a and 69 b, but preferably at least four thin sheets of piezoelectric material may be bonded/cofired together. The composite piezoelectric ceramic layer 69 may then be bonded to prestress layer(s) 64 with the adhesive layer(s) 66 and 66 a, and heated and cooled as described above to make a modified THUNDER transducer 12D. By having multiple thinner layers 69 a and 69 b of piezoelectric material in a modified transducer 12D, the composite ceramic layer generates a lower voltage and higher current as compared to the high voltage and low current generated by a THUNDER transducer 12 having only a single thicker ceramic layer 67. Additionally, a second prestress layer may be used comprise the same material as is used in the first prestress layer 64, or a material with substantially the same mechanical strain characteristics as described above, so that the composite piezoelectric ceramic layer 69 and the transducer 12D remain substantially flat, but still under a compressive stress.
  • Referring now to FIG. 2 b: Yet another alternate THUNDER generator element 12E includes another composite piezoelectric ceramic layer 169 that comprises multiple thin layers 169 a-f of PZT which are cofired together. In the cofired embodiment of FIG. 2 b, two or more layers 169 a-f, and preferably at least four layers, are used in this composite structure 12E. Each layer 169 a-f comprises a thin layer of piezoelectric material, with a thickness preferably on the order of about 1 mil, which are manufactured using thin tape casting for example. Each thin layer 169 a-f placed adjacent each other with electrode material between each successive layer. The electrode material may include metallizations, screen printed, electro-deposited, sputtered, and/or vapor deposited conductive materials. The individual layers 169 a-f and internal electrodes are then bonded to each other by cofiring the composite multi-layer ceramic element 169. The individual layers 169 a-f are then poled in alternating directions in the thickness direction. This is accomplished by connecting high voltage electrical connections to the electrodes, wherein positive connections are connected to alternate electrodes, and ground connections are connected to the remaining internal electrodes. This provides an alternating up-down polarization of the layers 169 a-f in the thickness direction. This allows all the individual ceramic layers 169 a-f to be connected in parallel. The composite piezoelectric ceramic layer 169 may then be bonded to prestress layer(s) 64 with the adhesive layer(s) 66 and 66 a, and heated and cooled as described above to make a modified THUNDER transducer 12D.
  • Referring again to FIGS. 2, 2 a and 2 b: By having multiple thinner layers 69 a and 69 b (or 169 a-f) of piezoelectric material in a modified transducer 12D-F, the composite ceramic layer generates a lower voltage and higher current as compared to the high voltage and low current generated by a THUNDER transducer 12 having only a single thicker ceramic layer 67. This is because with multiple thin paralleled layers the output capacitance is increased, which decreases the output impedance, which provides better impedance matching with the electronic circuitry connected to the THUNDER element. Also, since the individual layers of the composite element are thinner, the output voltage can be reduced to reach a voltage which is closer to the operating voltage of the electronic circuitry (in a range of 3.3V-10.0V) which provides less waste in the regulation of the voltage and better matching to the desired operating voltages of the circuit. Thus the multilayer element (bonded or cofired) improves impedance matching with the connected electronic circuitry and improves the efficiency of the mechanical to electrical conversion of the element.
  • A flexible insulator may be used to coat the convex face 12 a of the transducer 12. This insulative coating helps prevent unintentional discharge of the piezoelectric element through inadvertent contact with another conductor, liquid or human contact. The coating also makes the ceramic element more durable and resistant to cracking or damage from impact. Since LaRC-SI is a dielectric, the adhesive layer 67 a on the convex face 12 a of the transducer 12 may act as the insulative layer. Alternately, the insulative layer may comprise a plastic, TEFLON or other durable coating.
  • Electrical energy may be recovered from or introduced to the generator element 12 (or 12D) by a pair of electrical wires 14. Each electrical wire 14 is attached at one end to opposite sides of the generator element 12. The wires 14 may be connected directly to the electroplated 65 and 65 a faces of the ceramic layer 67, or they may alternatively be connected to the pre-stress layer(s) 64 and or 68. The wires 14 are connected using, for example, conductive adhesive, or solder 20, but most preferably a conductive tape, such as a copper foil tape adhesively placed on the faces of he electroactive generator element, thus avoiding the soldering or gluing of the conductor. As discussed above, the pre-stress layer 64 is preferably adhered to the ceramic layer 67 by LaRC-SI material, which is a dielectric. When the wires 14 are connected to the pre-stress layer(s) 64 and/or 68, it is desirable to roughen a face of the pre-stress layer 68, so that the pre-stress layer 68 intermittently penetrates the respective adhesive layers 66 and 66 a, and makes electrical contact with the respective electroplated 65 and 65 a faces of the ceramic layer 67. Alternatively, the Larc-SI adhesive layer 66 may have a conductive material, such as Nickel or aluminum particles, used as a filler in the adhesive and to maintain electrical contact between the prestress layer and the electroplated faces of the ceramic layer(s). The opposite end of each electrical wire 14 is preferably connected to an electric pulse modification circuit 10.
  • Prestressed flextensional transducers 12 are desirable due to their durability and their relatively large displacement, and concomitant relatively high voltage that such transducers are capable of developing when deflected by an external force. The present invention however may be practiced with any electroactive element having the properties and characteristics herein described, i.e., the ability to generate a voltage in response to a deformation of the device. For example, the invention may be practiced using magnetostrictive or ferroelectric devices. The transducers also need not be normally arcuate, but may also include transducers that are normally flat, and may further include stacked piezoelectric elements.
  • In the preferred embodiment of the present invention, the piezoelectric energy harvesting system 24 comprises a piezoelectric actuator element 12, electrical wires 14 and energy storage circuitry 10. In the preferred embodiment of the invention, the actuator element 12 is a flextensional piezoelectric transducer. Various constructions of flextensional piezoelectric transducers may be used (including, for example, “moonies”, “rainbows”, and other unimorph, bimorph, multimorph or monomorph devices, as disclosed in U.S. Pat. No. 5,471,721), but the actuator element 12 preferably comprises a Thin Layer Unimorph Driver and Sensor, “THUNDER™,” (as disclosed in U.S. Pat. No. 5,632,841) actuator constructed in accordance with the following description.
  • THUNDER actuators 12 are composite structures such as is illustrated in FIG. 1-2. Each THUNDER actuator 12 is preferably constructed with a PZT piezoelectric ceramic layer 67 which is electroplated 65 and 65 a on its two opposing faces. A steel, stainless steel, beryllium alloy or other metal first pre-stress layer 64 is adhered to the electroplated 65 surface on one side of the ceramic layer 67 by a first adhesive layer 66. The first adhesive layer 66 is preferably LaRC™-SI material, as developed by NASA-Langley Research Center and disclosed in U.S. Pat. No. 5,639,850. A second adhesive layer 66 a, also preferably comprising LaRC-SI material, is adhered to the opposite side of the ceramic layer 67. During manufacture of the THUNDER actuator 12 the ceramic layer 67, the adhesive layers 66 and 66 a and the first pre-stress layer 64 are simultaneously heated to a temperature above the melting point of the adhesive material, and then subsequently allowed to cool, thereby re-solidifying and setting the adhesive layers 66 and 66 a. During the cooling process the ceramic layer 67 becomes compressively stressed, due to the higher coefficient of thermal contraction of the material of the pre-stress layer 64 than for the material of the ceramic layer 67. Also, due to the greater thermal contraction of the laminate materials (e.g. the first pre-stress layer 64 and the first adhesive layer 66) on one side of the ceramic layer 67 relative to the thermal contraction of the laminate material(s) (e.g. the second adhesive layer 66 a) on the other side of the ceramic layer 67, the ceramic layer deforms in an arcuate shape having a normally concave face 12 a and a normally convex face 12 c. One or more additional pre-stressing layer(s) 64 a may be similarly adhered to either or both sides of the ceramic layer 67 in order, for example, to increase the stress in the ceramic layer 67 or to strengthen the actuator 12.
  • Electrical energy may be introduced to or recovered from the actuator element 12 by a pair of electrical wires 14 attached at one end to opposite sides of the actuator element 12. The opposite ends of the electrical wires 14 are connected to the electric energy storage circuitry 10. As discussed above, the pre-stress layers 64 and 64 a are preferably adhered to the ceramic layer 67 by LaRC-SI material. The wires 14 may be connected (for example by glue or solder 20) directly to the electroplated 65 and 65 a faces of the ceramic layer 67, or they may alternatively be connected to the pre-stress layers 64 and 64 a. LaRC-SI is a dielectric. When the wires 14 are connected to the pre-stress layers 64 and 64 a, it is desirable to roughen a face of each pre-stress layer 64 and 64 a, so that the pre-stress layers 64 and 64 a intermittently penetrate the respective adhesive layers 66 and 66 a, and make electrical contact with the respective electroplated 65 and 65 a faces of the ceramic layer 67.
  • In operation, as the wearer of the shoe walks or runs, each time the contact surface 34 of the sole portion 26 impacts the ground 44 or similar surface a first force (indicated by arrow 16 in FIG. 4) substantially normal to the contact surface 34 of the sole portion 26, deforms the section 36 of the sole portion 26 between the contact surface 34 and the piezoelectric element 12, which, in turn, deforms the piezoelectric element 12. By virtue of the piezoelectric effect, the deformation of the piezoelectric element 12 at each impact produces a pulse of electrical energy. The pulse or pulses of electrical energy are transmitted via the electrical wires 14 to the electrical energy storage circuitry 10.
  • As shown in FIGS. 3-8, a piezoelectric energy harvesting system 24 is advantageously disposed in or molded into a cavity 40 located in the sole portion 26, such that when the contact surface 34 of the sole portion 26 impacts the ground 44 or when the sole portion 26 is bent, the piezoelectric energy harvesting system 24 is actuated. It should be understood that the piezoelectric energy harvesting system 24 is mounted in the sole portion 26 substantially near the contact surface 34, such that the energy transferred to the piezoelectric energy harvesting system 24 by the impact or bending of the contact surface 34 with the ground 44 is maximized, and attenuation of said energy in the section 36 of the sole portion 26 between the ground 44 and the piezoelectric energy harvesting system 24 is minimized. The piezoelectric harvesting system 24 is preferably located in a rear portion 26 a or central bending portion 26 b, of the sole portion 26, but may advantageously be located anywhere in the sole portion 26 such as the front 26 c or central 26 b portions which are subject to deflective forces that may be transferred to the piezoelectric energy harvesting system 24.
  • Referring to FIGS. 3-4: in one embodiment of the energy harvesting system, the transducer 12 is preferably mounted within the recess 40 to the top portion of the recess 40 (adjacent the footbed). More specifically, as can be seen in FIG. 3, in this preferred embodiment one end of the transducer 12 is mounted to the top portion 43 of the recess 40 on its convex face, such that the free end 122 of the transducer 12 extends downwardly from the top 43 and back walls 42 towards the bottom 44 and front walls 41 of the recess 40. Alternatively, one end 121 of the transducer 12 is mounted to the bottom portion 44 of the recess 40 on its convex face, such that the free end 122 of the transducer 12 extends upwardly from the bottom and back walls towards the top and front walls of the recess 40. The free end 122 of the transducer 12 extends in proximity to but not in contact with the front wall 41 of the recess 40. On the front wall 41 of the recess 40 is mounted a deflector 72 which extends towards the back wall 42 of the recess 40 and in proximity to the free end 122 of the transducer 12. The deflector 72 extends into the cavity a distance past the end 122 of the actuator 12, and when the sole portion is bent, the actuator is rotated with respect to the deflector such that the end of the actuator is bent and deflected by the deflector 72. Conversely, when the sole portion is straightened from the bent position, the actuator 12 is again rotated with respect to the deflector 72 such that the end 122 of the actuator 12 is bent and deflected by the deflector 72. In yet another alternative embodiment, the end 121 of the transducer 12 may be mounted to the top or bottom walls in proximity to the front wall of the recess. The free end 122 extend upwardly from the bottom wall or downwardly from the top wall towards the back wall of the cavity 40, and the deflector 72 is mounted to the back wall in a similar manner as the front mounted deflector. Alternatively, the free end 122 of the generator may extend towards the wall opposite the wall to which it is mounted, and that wall may act as the deflector 72. For example, where the fixed end 121 of the piezoelectric generator element 12 is mounted to the top wall in proximity to the rear surface of the cavity 40, the free end 122 tends toward the front surface and bottom surface of the cavity 40. When the contact surface is bent, as by walking, the free end is deflected by the front surface or the bottom surface of the cavity 40. Likewise the free end 122 of the generator 12 may be deflected by the rear or top surfaces of the cavity if it is mounted to the front or bottom surfaces of the cavity 40.
  • Referring again to FIGS. 3 and 4: In operation, as shown in FIG. 4, when a force indicated by arrow 16 is applied to the transducer 12, the force deforms the electroactive layer 67 (via deformation of the resilient deformable section 36 of the sole 26. The force may be applied to the transducer 12 by mechanical means located within the sole portion of the footwear. Preferably, the force is applied by a mechanical deflector 72 (e.g., fulcrum, finger, a plucker, a plunger, striker, toggle or roller switch) capable of developing a mechanical impulse for application to and removal from the transducer 12. The mechanical impulse (or removal thereof) is of sufficient force to cause the transducer 12 to deform quickly and accelerate over a distance (approximately 10 mm), and upon release to oscillate between deflected positions about the undeflected position, which generates an electrical signal for harvesting/storage for later use or connection to electrical devices. Preferably the mechanical deflection means 72 is a plucker 72 which is stationary with respect to the sole portion 26 of the footwear, and an edge of the transducer 12 is applied to and released by the deflector 72 by virtue of the deformation of the sole portion to which the transducer 12 is attached. Alternately, the deflector 72 moves in response to the force on the contact surface and causes a deflection of the actuator/generator).
  • Now referring to FIGS. 5 and 6: In another embodiment of the energy harvesting system, the transducer 12 is preferably mounted within the recess 40 tthrough the front portion 41 of the recess 40. As can be seen in FIG. 5, in this embodiment one end of the transducer 12 is mounted to the front portion 41 of the recess 40, such that the convex face of the transducer 12 extends from the front wall 41 towards the top 43 and back walls 42 of the recess 40. The free end 121 of the transducer 12 extends in proximity to but not in contact with the back wall 42 of the recess 40. On the back wall of the recess 40 is mounted a deflector 72 which extends towards the front wall 41 of the recess 40 and in proximity to the free end 122 of the transducer 12. The deflector extends into the cavity a distance past the end of the actuator 12, and when the sole portion is bent, the actuator is rotated with respect to the deflector such that the end of the actuator is bent and deflected by the deflector 72. Conversely, when the sole portion is straightened from the bent position, the actuator 12 is again rotated with respect to the deflector 72 such that the end of the actuator 12 is bent and deflected by the deflector 72. Although the transducer end 121 may be mounted to the front wall 41 of the recess 40, it may also extend into the back wall 42 and the sole portion therebehind. The actuator 12 may be mounted to/within the back portion 42 such that the convex face of the actuator faces up, and extends upwardly from the back wall 42 towards the front wall 41 and top wall 43 of the recess with the deflector on the front wall 41 of the recess 40. In yet another embodiment the end 121 of the actuator 12 may be mounted to and/or within the front wall 41 of the recess with the free end extending toward the back wall 42, and with the convex face of the actuator 12 facing either the top wall 43 or the bottom wall 44 of the cavity. In this last embodiment, the deflector 72 is mounted to the back wall 42 of the recess.
  • In operation, as shown in FIG. 6, when a force indicated by arrow 16 is applied to the transducer 12, the force deforms the electroactive layer 67. The force may be applied to the transducer 12 by mechanical means located within the sole portion of the footwear. Preferably, the force is applied by a mechanical deflector 72 (e.g., a plucker, a plunger, striker, toggle or roller switch) capable of developing a mechanical impulse for application to and removal from the transducer 12. The mechanical impulse (or removal thereof) is of sufficient force to cause the transducer 12 to deform quickly and accelerate over a distance (approximately 10 mm), and upon release to oscillate between deflected positions about the undeflected position, which generates an electrical signal for harvesting/storage for later use or connection to electrical devices.
  • Preferably the mechanical deflection means 72 is a plucker 72 which is stationary with respect to the sole portion 26 of the footwear. The free end 122 of the transducer 12 is applied to and released from the deflector 72 by virtue of the deformation of the sole portion to which the opposite end 121 of the transducer 12 is attached.
  • Referring now to FIGS. 7-8: FIGS. 7-8 show an alternate embodiment of a deflector assembly mounted within the recess for deflection of the transducer 12. The deflector assembly comprises a pair of counter-rotating levers and a plucker assembly for deflecting the free end of the transducer 12. The motion of walking and bending the sole portion deflects one counter-rotating lever, to cause the other counter-rotating lever to push the paddle assembly against the free end 122 of the transducer 12. The end 122 of the transducer 12 is then released and caused to oscillate thereby generating an electrical signal.
  • More specifically, Referring now to FIGS. 9 a-c: FIGS. 11 a-c show the preferred embodiment of a base plate 70 with a deflector assembly 72 and containing the transducer 12. The transducer 12 is mounted with one end 121 of the transducer 12 placed between the surfaces the clamping and base plates 75 and 70 with fasteners 77 (screws, bolts, etc . . . ) such that the substrate 64 contacts both surfaces 75 a and 70 a. The ceramic layer 67 which extends above the surface of the substrate 64 on the convex face 12 a extends into the recessed area 80 of the base plate 70. This prevents the ceramic layer 67 from contacting the upper surface 70 a of the base plate 70, and cushions the ceramic layer 67 against the compliant layer 85 in the recess 80, thereby reducing potential for damage to the ceramic layer 67. A deflector assembly 72 is mounted on the base plate 70 above and to the sides of the transducer 12. This deflector assemble 72 has a lower profile than previously described deflector assemblies 72 by virtue of the use of two cooperating counter-rotating lever assembles 260, 270 and a plucker assembly 300.
  • Referring again to FIGS. 9 a-c: The deflector assembly comprises a swing arm 260, which is essentially a first lever mounted above the clamped end 121 of the transducer 12 and tending towards the free end 122. The swing arm 260 preferably has two pivot arms 261 and 262 connected by a cross bar 265. The pivot arms 261 and 262 tend from above the clamped end 121 of the transducer 12 and tending towards the free end 122 of the transducer 12, along each side of the transducer 12 to prevent contact therebetween. A first end 261 a, 262 a of each pivot arm 261, 262 is connected to the two ends of a cross bar 265, which is situated above the clamping plate 75. Each pivot arm 261, 262, has a pin 264 extending outwardly from the transducer 12, located centrally on the pivot arms 261, 262. The pins are pivotably mounted within fulcrum clips 268, which allows the swing arm assembly 260 to pivot about the pins 264 and the fulcrum clips 268. The ends 261 b, 262 b of the pivot arms 261, 262 opposite the crossbar 265 are preferably upwardly curved to tend substantially vertically, or more preferably slightly off vertical and towards the free end 122 of the transducer 12 and rocker arm 270 assemblies. The curved ends 261,b, 262 b of the pivot arms 261, 262 may alternately be C-shaped, i.e., first curve downwardly (towards the base plate 70, and then upwardly. To accommodate the downward curve of the pivot arm ends 261 b, 262 b, the base plate 70 may contain recesses (not shown) within which the curved ends 261 b, 262 b may housed.
  • Referring again to FIGS. 9 a-c: The deflector assembly also comprises a rocker assembly 270, which is essentially a pair of second levers 271, 272 mounted above the free end 122 of the transducer 12 and tending towards and beyond the free end 122. The rocker assembly 270 preferably has two rocker arms 271 and 272 pivotably mounted to contact both the pivot arms 261, 262 and the plucker assembly 300. The rocker arms 271 and 272 tend from above the curved ends 261 b, 262 b of the pivot arms 261, 262 and tend towards and slightly beyond the free end 122 of the transducer 12, and along each side of the transducer 12 to prevent contact therebetween. Each of the rocker arms 271, 271 has a pin 274 thereon, extending outwardly from the transducer 12. Each of these pins 274 is pivotably mounted within a pivot hole 278 of the plucker housing 290. This allows each rocker arm 271, 272, to rotate about its respective pin 274 in response to a force on either end 271 a, 272 a, 271 b, 272 b of the rocker arm 271, 272. Each first end 271 a, 272 a of the rocker arms 271, 272 is in contact with the second ends 261 b, 262 b of the pivot arms 261, 262. When the crossbar 265 is depressed, the second ends 261 b, 262 b of the pivot arms 261, 262 move upwardly and contact the first ends 271 a, 272 a of the rocker arms 271, 272, causing the rocker arms 271, 272 to rotate about the rocker arm pins 274. This causes the second ends 271 b, 272 b of the rocker arms 271, 272 to be depressed.
  • Referring again to FIGS. 9 a-c: The deflector assembly also comprises a plucker assembly 300, which is essentially a slidably mounted curved paddle situated above the free end 122 of the transducer 12. The plucker assembly 300 is in contact with the rocker assembly 270 and is adapted to side downwardly within a pair of grooves in response to a downward motion from the second ends 271 b, 272 b of the rocker arms 271, 272. More specifically, the plucker assembly 300 comprises a plucker paddle 301, situated above and in contact with the free end 122 of the transducer 12. Connected to each end 300 a, 300 b of the plucker paddle 301 is a roller 305, which is in contact with the rocker arms 271, 272. Tending outwardly from each roller 305 is a slide pin 304. The slide pins 304 are slidably mounted within slide grooves 308 in the plucker housings 290. The slide grooves 308 tend from a maximum vertical position and downwardly away from the free end 122 of the transducer 12 to a minimum position beyond the free end 122 of the transducer 12. Thus, when the plucker assembly 300 is moved downwardly, the slide pins 304 and slide grooves 308 cause the plucker paddle 301 to move simultaneously downward and away from the free end of 122 the transducer 12.
  • Thus, when the crossbar 265 is depressed, the second ends 261 b, 262 b of the pivot arms 261, 262 move upwardly and contact the first ends 271 a, 272 a of the rocker arms 271, 272, causing the rocker arms 271, 272 to rotate about the rocker arm pins 274. This causes the second ends 271 b, 272 b of the rocker arms 271, 272 to be depressed. As the second ends 271 b, 272 b of the rocker arms 271, 272 are depressed, they contact the rollers 305 with a downward force, and the plucker assembly 300 is guided by the slide pins 304 and slide grooves 308 to cause the plucker paddle 301 to move simultaneously downward and away from the free end of 122 the transducer 12. The minimum or lowest position of the plucker assembly is beyond the free end 122 of the transducer 12, and therefore, as the plucker paddle 301 moves downward and outward, the free end 122 of the transducer 12 is released by the plucker paddle 301. Thus as the plucker assembly is depressed, the free end 122 of the transducer 12 is depressed from its neutral position 291 to a deflected position 292 at which position the paddle 301 releases the free end 122 of the transducer 12. The free end 122 of the transducer 12 then oscillates between positions 291 and 292.
  • Referring now to FIG. 9 c: The plucker paddle 301 preferably has an edge 301 a that contacts the free end 122 of the transducer 12 that has a radius in both in the thickness dimension (i.e., vertically corresponding to the thickness of the transducer 12 edge) and the transverse dimension (i.e., horizontally corresponding to the length of the transducer 12 edge) in order to advantageously release the free end 122 very quickly, i.e., without dragging across the end 122 of the transducer 12, which slows its release. It has been found that the more quickly and cleanly you release the end 122 of the transducer 12 during a “pluck”, the greater the output. This increases output without increasing the required plucking force. To be precise, the energy developed by the piezoelectric element 67 has been found to be a function of the acceleration of the piezoelectric element 67, rather than the speed of the “pluck.” It is possible “pluck” very slowly, and get excellent performance, so long as the piezoelectric element 67 is released fully and completely and as nearly instantly as possible. To determine the desired shape of the tip 301 a of the plucker paddle 301, several plucker paddles were designed and released very, very slowly, in attempting to get a quick “release” of the end 122 of the transducer 12. If the plucker paddle 301 did not have a radius on the tip, but instead had a rectangular shape, it was found that the end 301 a of the plucker paddle 301 (the thickness dimension) actually “dragged” across the edge 122 of the transducer 12, slowing the release, and decreasing the electrical output. Thus, increasing the rate of “release” of the element's edge 122 improved the acceleration and the output. Thus, the radius of the tip 301 a (in the thickness dimension) of the “plucker” paddle 301 contributes substantially to how quickly the transducer 12 edge 122 gets off the paddle. This has been shown to have a direct effect on electrical performance, because a smaller radius equates to a quicker “release” which equates to greater electrical output. If the paddle 301 is manufactured from sufficiently hard materials, or is hardened, the edge 301 a of the paddle 301 can be made with an even smaller radius. The tip 301 a of the plucking paddle 301 may be coated with a very hard material with low friction, thereby lowering the plucking resistance. This approach can prove to be useful in increasing the power output of a transducer 12 without increasing the required displacement or amount of bending, and may allow the generation of the same amount of energy with lower “button force” by the user of the device, as well as being useful in increasing wear resistance for applications requiring many hundreds of thousands of switch cycles.
  • The transducer 12 is typically is curved along its length, i.e., the longitudinal dimension and this curvature allows the element 12 to be bent or “plucked” substantially before it reaches a flattened state. The transducer 12 is also curved across its transverse dimension, i.e., the transverse dimension normal to the thickness and longitudinal dimensions. To ensure a quick “release”, the shape of the edge 301 a of the plucking paddle 300 should generally match this transverse curve. The radius curvature of the transducer 12 in the transverse plane is approximately 6 inches, and therefore the same radius should be used for the curve edge 301 a in the transverse plane of the paddle 301. Different sized transducers 12 will have higher or lower transverse radii of curvature, so regardless of the size of the transducer 12, the radius of curvature for the curved edge 301 a in the transverse plane of the paddle 301 should substantially match the transverse curvature of the transducer 12.
  • Although both paddle 301 dimensions affect durability, and both dimensions affect performance, the tip radius has more of an effect on element 12 performance, while the transverse curve has a greater effect on the element's 12 substrate wear, and therefore is more of an influence on its life expectancy. This is because the transverse radius determines how much of the paddle 301 contacts the element 12. A greater contact area is equates with less wear and longer substrate life, i.e., durability. As stated above, by manufacturing the paddle 301 from sufficiently hard or hardened materials, the edge 301 a of the paddle 301 can be made with very small radius. The tip 301 a of the plucking paddle 301 may be coated with a very hard material with low friction, thereby lowering the plucking resistance. Hardened, low friction materials are useful in increasing the power output of a transducer 12 without increasing the required displacement or amount of bending, or allowing the generation of similar electrical energy output with lower “button force”, and increasing wear resistance.
  • Referring again to FIGS. 9 a-c: In order to return the deflector assembly 72 to its normal elevated position, the levers 260, 270 and/or plucker assembly 300 are preferably spring loaded. More specifically, one or more springs 310 are located in contact with the deflector assembly 72, and are placed in compression or tension upon actuation of the assembly 72, which springs' 310 restoring force is used to return the deflector assembly 72 to its neutral position. As shown in FIGS. 11 a-c, in the preferred embodiment of the invention, two springs 310 are located within cavities 320 in the plucker housings 290, below the pins 304. For simplicity of illustration, the springs 310 are shown as coiled springs 310, but are preferably leaf springs 310. Upon downward deflection of the crossbar 265 and thereby the pivot bar assembly 260 and rocker assembly 270, the pins 304 travel down the grooves 308 and compress the springs 310 in the cavities 320. Upon release of pressure from the crossbar 265, the springs 310 restore the pivot bar 260, rocker bars 270 and plucker 300 to their undeflected positions. While the springs 310 shown are in the housings 290, other placements of the springs 310 may also be desirable, including, for example: spring(s) 310 may be placed beneath the cross bar 265, on either side of the fulcrum 268 of the pivot bars 261, 262 or rocker arms 270; one or more rotational or clock springs 310 may be placed on the pins 264 of the pivot bars 261, 262, on the pins 274 of the rocker arms 271, 272, on the pivot bar fulcrums 268, or the rocker arm pin holes 278; springs 310 may be placed in the groove 308 or recess 320 above or below the plucker bar pins 304; one or more springs 310 may be attached to the plucker bar 301; and the opposing side of the spring 310 (not attached to the deflector assembly 72) may be attached to the base plate 70, the plucker housing 290, the fulcrum 268 or to another part of the deflector assembly 72 to restore it to its undeflected position.
  • Referring now to FIGS. 10 a-e: To facilitate efficient plucking and maximize vibration of the transducer 12, the plucker assembly is preferably configured so as to rotate during each actuation and to cock after each actuation. Specifically, with a triangularly shaped plucker paddle 301, any one of the three faces 301 b, 301 c, 301 d of the plucker paddle 301 (having a substantially triangular cross-section) may engage the edge of the transducer. As the plucker paddle 301 moves downward and outward from the transducer edge, a rotation mechanism (including a pin 445 and radial ridge 444 as shown in the figures) causes the plucker paddle edge to rotate away from the transducer edge 122. As the plucker paddle rotates, it reaches a point where the transducer edge 122 is released. Since the plucker paddle 301 has rotated, it also does not interfere with the vibration of the transducer edge. When the downward force is removed from the plucker assembly, the spring loaded plucker paddle 301 is returned upward towards its starting position, and rotates until the radial ridge 444 contacts a rotational stop 443, so that the plucker paddle 301 is again is a position to engage the transducer edge.
  • Referring again to FIGS. 10 a-e: More specifically, the plucker paddle 301 is shaped substantially like a triangular prism. In the center of each triangular face of the paddle is a pin 304 that travels along the groove 308 in the plucker housing. Each triangular face of the paddle also preferably has threes raised ridges 444 thereon extending from the center of the triangular face outwardly towards the edges of the triangular faces adjacent the flat paddle surfaces and most preferably towards each apex of the triangular faces. The plucker housings each have a vertical ridge or pin 443 against which the raised ridge rests when the plucker paddle is in its maximum position. This maintains the bottom surface of the plucker paddle (opposite the apex bisected by the raised ridge) in an essentially horizontal position above and/or against the edge of the transducer 12.
  • A force applied to the deflector assembly 72 described above causes the piezoelectric transducer 12 to deform from position 291 to position 292 and by virtue of the piezoelectric effect, the deformation of the piezoelectric element 67 generates an instantaneous voltage between the faces 12 a and 12 c of the transducer 12, which produces an electrical signal. Furthermore, when the force is removed from the piezoelectric transducer 12, i.e., when released by the plucker assembly 300 at position 292, the transducer 12 oscillates between positions 291 and 292 until it gradually returns to its original shape. As the transducer 12 oscillates, the ceramic layer 67 strains, becoming alternately more compressed and less compressed. The polarity of the voltage produced by the ceramic layer 67 depends on the direction of the strain, and therefore, the polarity of the voltage generated in compression is opposite to the polarity of the voltage generated in tension. Therefore, as the transducer 12 oscillates, the voltage produced by the ceramic element 67 oscillates between a positive and negative voltage for a duration of time. The duration of the oscillation, and therefore the duration of the oscillating electrical signal produced, is preferably in the range of 100-250 milliseconds, depending on the shape, mounting and amount of force applied to the transducer 12. The wave form of the oscillating voltage is illustrated in FIG. 12 a.
  • As previously mentioned, the applied force causes the piezoelectric transducer 12 to deform. By virtue of the piezoelectric effect, the deformation of the piezoelectric element 67 generates an instantaneous voltage between the faces 12 a and 12 c of the transducer 12, which produces a pulse of electrical energy. Furthermore, when the force is removed from the piezoelectric transducer 12, the transducer 12 recovers its original arcuate shape. This is because the bending of the substrate (and attached layers) stores mechanical (spring) energy which is released upon removal of the force. Additionally, the substrate or prestress layers 64 and 68 to which the ceramic 67 is bonded exert a compressive force on the ceramic 67, and the transducer 12 thus has an additional restoring force that causes the transducer 12 to return to its undeformed neutral state. On the recovery stroke of the transducer 12, the ceramic 67 returns to its undeformed state and thereby produces another electrical pulse of opposite polarity. The downward (applied) or upward (recovery) strokes cause a force over a distance that is of sufficient magnitude to create the desired electrical pulse. The duration of the recovery stroke, and therefore the duration of the pulse produced, is preferably in the range of 50-100 milliseconds, depending on the mechanical properties of the transducer, including its natural frequency of vibration.
  • In the preferred embodiment of the invention, the transducer 12 is clamped at one end 121 and the mechanical impulse is applied to the edge on the free end 122, i.e., at the end opposite to the clamped end 121 of the transducer 12. By applying the force to the edge on the free end 122 of the transducer 12 and releasing it, the actuator oscillates between the release position, to another position past the undeformed position, and then oscillates (in a dampened manner) between the deformed positions while returning to the undeformed position, by virtue of the substrate's (spring steel) restoring force. Therefore, the electrical pulse that is generated upon removal of the force is an oscillating wave (rather than a single pulse as with the prior actuating means disclosed above).
  • The applied force causes the piezoelectric transducer 12 to deform and by virtue of the piezoelectric effect, the deformation of the piezoelectric element 67 generates an instantaneous voltage between the faces 12 a and 12 c of the transducer 12, which produces an electrical signal. Furthermore, when the force is removed from the piezoelectric transducer 12, the transducer 12 oscillates between positions 291 and 292 until it gradually returns to its original shape. As the transducer 12 oscillates, the ceramic layer 67 strains, becoming alternately more compressed and less compressed. The polarity of the voltage produced by the ceramic layer 67 depends on the direction of the strain, and therefore, the polarity of the voltage generated in compression is opposite to the polarity of the voltage generated in tension. Therefore, as the transducer 12 oscillates, the voltage produced by the ceramic element 67 oscillates between a positive and negative voltage for a duration of time. The duration of the oscillation, and therefore the duration of the oscillating electrical signal produced, is preferably in the range of 100-500 milliseconds, depending on the shape, mounting and amount of force and number of plucks applied to the edge of the transducer 12.
  • The electrical signal generated by the transducer 12 is applied to downstream circuit elements 10 via wires 14, and conductive foil, solder or conductive adhesive connected to the transducer 12. More specifically, a first wire 14 is connected to the electrode 90 which extends into the recess 80 and contacts the electrode 68 on the convex face 12 a of the transducer 12 or to a foil adhered to the lower face 12 a of the transducer 12. Preferably the wire 14 is attached to a conductive foil (not shown) adhered to the face 12 a of the transducer 12 situated above the recess 80 and compliant layer 85. Alternately, the wire 14 is connected to the electrode 90 outside of the recess close to the end of the base plate 70 opposite the end having the clamping member 75. A second wire 14 is connected directly to the first prestress layer 64, i.e., the substrate 64 which acts as an electrode on the concave face 12 c of the transducer 12.
  • Referring now to FIGS. 11 a-e: To facilitate efficient plucking and maximize vibration of the transducer 12, an alternate plucker assembly is configured not only to rotate during each actuation and to cock after each actuation, but to also pluck the end of the transducer twice. Specifically, with a “double plucker” paddle comprises a paddle with six apexes 301 a, and any one of the six downward facing faces of the plucker paddle apexes (each having a substantially triangular cross-section) may engage the edge 122 of the transducer. As the “double plucker” paddle moves downward and outward from the transducer edge, a rotation mechanism (including a pin 445 and radial ridge 443 as shown in the figures) causes the edge 301 a of a first apex of the “double plucker” paddle to rotate away from the transducer edge 122. As the plucker paddle 301 rotates, it reaches a point where the transducer edge 122 is released. Since the “double plucker” paddle has rotated, it also does not interfere with the vibration of the transducer edge 122. This allows the transducer to vibrate for a duration of time, preferably on the order of 75-150 milliseconds.
  • As the “double plucker” paddle continues to move downward and outward from the transducer edge 122, the rotation mechanism (including a pin 445 and radial ridge 444 as shown in the figures) causes the edge 301 a of the second apex of the “double plucker” paddle to reengage the end 122 of the transducer, after it has vibrated for a duration, preferably for at least 75 milliseconds. As the “double plucker” paddle continues to rotate, it reaches a point, once again, where the transducer edge 122 is released. Since the “double plucker” paddle has rotated, it also does not interfere with the vibration of the transducer edge 122, which vibrates for an additional 75-250 milliseconds. When the downward force is removed from the “double plucker” assembly, the spring loaded “double plucker” paddle is returned upward towards its starting position, and rotates until the radial ridge 444 contacts a rotational stop 443, so that the “double plucker” paddle is again is a position to engage the transducer edge, with the third and fourth apex edges.
  • Referring again to FIGS. 11 a-e: More specifically, the “double plucker” paddle is shaped substantially like a six pointed star prism, similar to the “Star of David” with the apexes offset to allow two successive engagements of the transducer edge, while allowing the transducer edge to vibrate between successive engagements without interference from the plucker paddle edges. In the center of each star face of the paddle is a pin that travels along the groove in the plucker housing. Each star face of the paddle also preferably has three raised ridges thereon extending from the center of the star face outwardly towards the edges of the faces adjacent the flat paddle surfaces and most preferably towards alternate apexes of the six point star faces. The plucker housings each have a vertical ridge or pin against which the raised ridge rests when the plucker paddle is in its maximum position. This maintains the bottom surface of the plucker paddle (opposite the apex bisected by the raised ridge) in an essentially horizontal position above and/or against the edge of the transducer 12.
  • A force applied to the deflector assembly 72 described above causes the piezoelectric transducer 12 to deform from position 291 to position 292 and by virtue of the piezoelectric effect, the deformation of the piezoelectric element 67 generates an instantaneous voltage between the faces 12 a and 12 c of the transducer 12, which produces an electrical signal. Furthermore, when the force is removed from the piezoelectric transducer 12, i.e., when released by the first apex of the “double plucker” assembly 300 at position 292, the transducer 12 oscillates between positions 291 and 292 for a duration of time, but before the amplitude of the oscillation has dropped below a level corresponding to a desired threshold output voltage. Furthermore, when the force from the second apex applied and removed from the piezoelectric transducer 12, i.e., when released by the second apex of the “double plucker” assembly 300 at position 292, the transducer 12 oscillates between positions 291 and 292 until it gradually returns to its original shape. As the transducer 12 oscillates, the ceramic layer 67 strains, becoming alternately more compressed and less compressed. The polarity of the voltage produced by the ceramic layer 67 depends on the direction of the strain, and therefore, the polarity of the voltage generated in compression is opposite to the polarity of the voltage generated in tension. Therefore, as the transducer 12 oscillates, the voltage produced by the ceramic element 67 oscillates between a positive and negative voltage for a duration of time. The duration of the oscillation, and therefore the duration of the oscillating electrical signal produced, is preferably in the range of 150-350 milliseconds, depending on the shape, mounting and amount of force applied to the transducer 12. The wave form of the oscillating voltage is illustrated in FIG. 12 d. The rectified waveform is shown in FIG. 12 e and the regulated waveform is shown in FIG. 12 f.
  • The electrical signal from the wires 14 connected to the generator/transducer 12 is applied to energy storage circuitry 10 including capacitors and/or batteries. Furthermore the electrical signal is preferably rectified, most preferably using a full bridge rectifier. The output signal of the rectifier may also be input into a voltage regulator in order to control the amount of voltage applied to the energy storage element.
  • Referring now to FIGS. 13-15: The transducer 12 is first connected to a rectifier 31. Preferably the rectifier 31 comprises a bridge rectifier 31 comprising four diodes D1, D2, D3 and D4 arranged to only allow positive voltages to pass. The first two diodes D1 and D2 are connected in series, i.e., the anode of D1 connected to the cathode of D2. The second two diodes D3 and D4 are connected in series, i.e., the anode of D3 connected to the cathode of D4. The anodes of diodes D2 and D4 are connected, and the cathodes of diodes D1 and D3 are connected, thereby forming a bridge rectifier. The rectifier is positively biased toward the D2-D4 junction and negatively biased toward the D1-D3 junction. One of the wires 14 of the transducer 12 is electrically connected between the junction of diodes D1 and D2, whereas the other wire 14 (connected to the opposite face of the transducer 12) is connected to the junction of diodes D3 and D4. The junction of diodes D1 and D3 are connected to ground. A capacitor C11 is preferably connected on one side to the D2-D4 junction and on the other side of the capacitor C11 to the D1-D3 junction in order to isolate the voltages at each side of the rectifier from each other. Therefore, any negative voltages applied to the D1-D2 junction or the D3-D4 junction will pass through diodes D1 or D3 respectively to ground. Positive voltages applied to the D1-D2 junction or the D3-D4 junction will pass through diodes D2 or D4 respectively to the D2-D4 junction. The rectified waveform is shown in FIG. 10 b.
  • The circuit also comprises a voltage regulator U2, which controls magnitude of the input electrical signal downstream of the rectifier 31. The rectifier 31 is electrically connected to a voltage regulator U2 with the D2-D4 junction connected to the Vin pin of the voltage regulator U2 and with the D1-D3 junction connected to ground and the ground pin of the voltage regulator U2. The voltage regulator U2 comprises for example a LT1121 chip voltage regulator U2 with a 3.3 volts DC output. The output voltage waveform is shown in FIG. 12 c and comprises a substantially uniform voltage signal of 3-12 volts having a duration of approximately 100-250 milliseconds, depending on the load applied to the transducer 12. The regulated waveform is shown in FIG. 12 b. Each of these output waveforms is the result of successive footfalls. Therefor the energy storage element is successively charged with this waveform upon each footfall.
  • The output voltage signal from the voltage regulator (at the Vout pin) may then be transmitted via another conductor to the capacitor or battery. For example, long life rechargeable batteries 430 may be included in the circuitry and may be recharged through the electromechanical transducers 12. These rechargeable batteries 430 may thus provide stored or backup power to the an electrical device 50 connected to the output terminals of the battery 430. In the circuit of FIGS. 13 and 14, the ground terminal of the battery is electrically connected to ground and the positive terminal is connected to the output side of the rectifier before the voltage regulator. In the preferred circuit of FIGS. 13 and 15, the ground terminal of the battery is connected to ground and the positive terminal is connected to the output side of the voltage regulator U2 before the electrical device 50.
  • Referring again to FIGS. 13-15: The circuit of FIG. 14 includes a rechargeable battery as in the circuit of FIG. 13. However, in this circuit, the output of the voltage regulator U2 is connected only to the positive/charging terminal of the rechargeable battery 430. The output of the rechargeable battery 430 is connected to the input side of a portable electronic device through a switch S1. The switch S1 may comprise a transistor. When the switch is closed/energized, electrical power is applied to the electronic device. The switch may be energized when the deflection means activates the transducer 12. When the transducer 12 is deflected, an electrical output is produced, most of which is rectified and regulated, and then used of charge the battery 430. A small amount of the electrical power is tapped by a filter/trigger from the transducer 12 (using for example a BJT connected between a grounded resistor and a second resistor between the BJT and the transducer 12), which electrical energy is applied to the switching device S1 in order to electrically connected the battery to the transmitter subcircuit.
  • The electrical storage circuitry also has an output by which the stored energy may be used to power electrical devices 50 such as radios, transmitters, receivers, GPS devices and the like. To facilitate the use of the stored electrical energy, the energy storage element has a positive connection 432 and a ground connection 431 which may simply consist of two wires. Preferably, the wires are further connected to a power jack to which these electrical devices may be connected. Examples of these connections include plug and socket connection and RCA jacks, coaxial and uniaxial power jacks and the like. Plugging of the device 50 into the power jack across the output terminals 431, 432 of the battery 430 may be provide the electrical contact to close a switch S1 connected to the output (positive terminal) of the battery 430.
  • While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Many other variations are possible, for example: More than one piezoelectric element 12 may be employed; The electrical energy storage circuitry 10 may comprise an amplifier, for amplifying the voltage applied to the piezoelectric element(s) 12; The electrical energy storage circuitry 10 may comprise a capacitor or capacitors for storage of the electrical energy; The piezoelectric element may comprise a either flat or arcuate ferroelectric gernerators.
  • Accordingly, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents.

Claims (1)

1. An energy harvesting system comprising:
An article of footwear comprising a shoe upper member having a bottom edge, a sole member having a footbed, a contact surface, a heel portion, an instep portion, and a deformable resilient section;
said bottom edge of said shoe upper member being attached to said footbed;
said sole member having a cavity between said contact surface and said footbed, said cavity having an upper surface opposite a lower surface, and a front surface opposing a back surface;
said deformable resilient section being disposed between said lower surface of said cavity and said contact surface; and
a piezoelectric generator apparatus within said cavity having a first end and a second end and having first and second electroded major faces;
said first end of said piezoelectric generator apparatus being mounted to said front surface, said back surface, said upper surface or said lower surface;
said second end of said piezoelectric generator apparatus being located in said cavity opposite to said front surface, said back surface, said upper surface or said lower surface to which said first end of said piezoelectric generator apparatus is mounted;
a deflector assembly within said cavity adjacent said second end of said piezoelectric generator apparatus; and
energy storage means for storing piezoelectric electrical energy, said energy storage means being in electrical communication with each of said first and second electroded major faces;
whereby, upon application of a first force to said contact surface, said first force causes a deformation of said deformable resilient section;
and whereby said deformation of said resilient deformable section causes a deformation of said second end of said piezoelectric generator apparatus by said deflector assembly, thereby generating piezoelectric electrical energy with said piezoelectric generator apparatus.
US11/184,588 2004-07-19 2005-07-19 Footwear incorporating piezoelectric energy harvesting system Abandoned US20060021261A1 (en)

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