Method and apparatus for mechanical energy harvesting using variable inductance magnetic flux switch

A method of mechanical-to-electrical energy conversion utilizes a mechanical spring in combination with a rapid-action variable inductance magnetic flux switch to convert a spring-loaded mechanical energy into a change in magnetic flux captured by an electrical coil element within the magnetic flux switch. The change in coil inductance and magnetic flux induces a current to flow through the electrical coil in the form of a a pulse of electrical energy that may be stored. The electrical coil is coupled to the mechanical spring so that each time the spring is released, the coil moves with respect to a magnetic core and a change in flux is created. The application of an external mechanical force (such as human locomotion) functions to compress and subsequently “unlock” the mechanical switch, allowing for the electrical energy associated with the application of aperiodic forces to be harvested.

TECHNICAL FIELD

The present invention relates to mechanical energy harvesting and, more particularly, to the utilization of a variable inductance magnetic flux switch to convert mechanical energy (e.g., spring force) into electrical energy that can be stored for later use as needed.

BACKGROUND OF THE INVENTION

Currently, the majority of autonomous and mobile electronic systems are powered by electrochemical batteries. Although the battery quality has substantially improved over the last two decades, their energy density has not greatly increased. At present, factors such as cost, weight, limited service time, and waste disposable problems (all intrinsic to the materials used to create batteries) are impeding the advance of many areas of electronics. The problem is especially acute in the portable electronics space, where rapidly growing performance and sophistication of mobile electronic devices leads to ever-increasing power demands that electrochemical batteries are unable to meet.

One of the technologies that holds great promise to substantially alleviate today's reliance on electrochemical batteries is high-power energy harvesting. The concept of energy harvesting works towards developing self-powered devices that do not require replaceable power supplies. In cases where high mobility and high-power output is required, harvesters that convert mechanical energy into electrical energy are particularly promising as they can tap into a variety of high-power-density energy sources, including mechanical vibrations, human and machine motion, etc.

High-power harvesting of mechanical energy is a long-recognized concept which has not been commercialized in the past due to the lack of a viable energy harvesting technology. Existing methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric, or electrostatic do not allow effective direct coupling to the majority of high-power environmental mechanical energy sources. Bulky and expensive mechanical or hydraulic transducers are required to convert a broad range of aperiodic forces and displacements typically encountered in nature into a form accessible for conversion using those methods. Thus, any method of mechanical-to-electrical energy conversion that can provide effective coupling to a broad range of forces and displacements would be highly beneficial as it would allow energy harvesting to extend into a wider range of environments. Many practical applications would benefit from such energy conversion methods, including, for example, lower and upper limb prosthetic devices, energy harvesting from human motion, including human locomotion, internet-of-things devices, and the like.

SUMMARY OF THE INVENTION

The needs remaining in the art are addressed by the present invention, which relates to mechanical energy harvesting and, more particularly, to the utilization of a variable inductance magnetic flux switch, where magnetic flux is generated in response to the movement of a spring-loaded electrical coil through a magnetic field.

As described in detail below, the present invention is directed to a method of mechanical-to-electrical energy conversion utilizing an inventive apparatus comprising a mechanical energy storage device (such as a mechanical spring) that is used in combination with a rapid-action variable inductance magnetic flux switch to convert a spring-loaded mechanical energy into a change in magnetic flux that is converted into a pulse of electrical energy that may be stored.

In exemplary embodiments of the present invention, the variable inductance magnetic flux switch comprises a movable coil and a stationary magnetic core. The mechanical spring is used to control the movement of the coil with respect to the magnetic core so as to change the amount of magnetic flux captured by the coil as well as the coil inductance, the changes in flux and inductance inducing a current to flow through the coil, which exits the coil as a pulse.

Various embodiments may use a single magnetic core element, or a pair of oppositely-poled magnetic core elements to control the amount of energy that is harvested by the action of the mechanical spring. Different means for unlocking and re-locking the mechanical spring are proposed and used to allow the energy harvesting to proceed without the need for a separate process to re-start a subsequent energy collection cycle. Said another way, the actuation process is self-initiated by a resettable switching mechanism once the spring displacement or force exceeds a certain predefined value.

It is an aspect of the present invention that the use of a variable inductance magnetic flux switch, as described in detail below, provides effective coupling to a broad range of forces and displacements.

A method implemented in accordance with the present invention allows for many currently un-accessible mechanical energy sources to be involved in a process of conversion into electrical energy. The method of the present invention is particularly well-suited for extracting energy from sources characterized by relatively slow aperiodic motion with high forces and low displacements, such as those encountered in human locomotion and lower limb prosthetic devices.

An exemplary embodiment of the present invention takes the form of an apparatus for harvesting electrical energy from motion associated with mechanical energy, comprising a mechanical spring disposed within a housing; and a variable inductance magnetic flux switch positioned within an open central area of the housing. The variable inductance magnetic flux switch itself is formed to include a stationary magnetic core component and a movable electrical coil subassembly disposed to surround the stationary magnetic core component The movable electrical coil subassembly is coupled to the mechanical spring in a manner such that movement of the mechanical spring also provides movement of the electrical coil subassembly. A plunger is disposed over the combination of the stationary magnetic core component and the movable electrical coil subassembly, where the plunger is responsive to the application of an external force to move the variable inductance magnetic flux switch downward and into the housing and compressing the mechanical spring. The apparatus also includes a spring lock mechanism for releasing the mechanical spring when in a compressed state, providing movement of the mechanical spring and coupled electrical coil subassembly, where the movement of the electrical coil subassembly with respect to the stationary magnetic core creates a change in the magnetic flux captured by the electrical coil subassembly, as well as the coil subassembly inductance, and induces a flow of electrical current for storage as the output of the apparatus.

Yet another embodiment of the present invention may be defined in terms of a method of harvesting electrical energy from mechanical movement, comprising the steps of: (1) providing a variable inductance magnetic switch including a stationary magnetic core component and a movable electrical coil subassembly disposed to surround the stationary magnetic core component; (2) providing a mechanical spring coupled to the movable electrical coil; (3) impressing a force on the coupled mechanical spring and movable electrical coil so as compress the mechanical spring; and (4) unlocking the compressed mechanical spring to cause movement of the released mechanical spring and coupled electrical coil subassembly, where the movement of the electrical coil subassembly with respect to the stationary magnetic core creates a change in the magnetic flux captured by the electrical coil subassembly and the change in the coil inductance, thereby inducing a flow of electrical current therethrough.

Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.

DETAILED DESCRIPTION

As mentioned above and will be described in detail below, the present invention relates to an apparatus and method for harvesting electrical energy from mechanical energy that utilizes a magnetic flux switch formed of a centrally-located magnetic core and an electrical coil disposed to surround the magnetic core. A mechanical spring is attached to a structure supporting the electrical coil and accumulates mechanical energy as it is compressed. When the tension force holding the spring in compression is overcome (i.e., the spring is “unlocked”), the electrical coil translates longitudinally with the respect to the magnetic core. The movement of the electrical coil with respect to the stationary magnetic core is sufficient to change the amount of magnetic flux captured by coil and thus induce an electric current to flow within the coil. This current (typically in the form of pulses) may then be immediately used, or stored in a battery/capacitor for later use, as needed.

The inventive apparatus operates on the application of an external force to both compress the mechanical spring and then “unlock” the compressed spring to initiate the movement of the electrical coil. Therefore, a relatively slow, aperiodic motion involving a high magnitude force with minimal displacement is contemplated as able to control the inventive apparatus and generate electrical energy in response to this motion. Indeed, It is contemplated that human motion is one exemplary mechanical force that may be applied to the mechanical spring to initiate the operation of the inventive apparatus. Besides the inducement of an electric current by the change in flux passed through the coil area, the change in the coil's inductance as a function of its movement with respect to the magnetic core is a second mechanism that also induces the flow of current through the coil.

FIG. 1is an external view of an exemplary energy harvesting apparatus10formed in accordance with one exemplary embodiment of the present invention, withFIG. 2being a cross-sectional view that illustrates the various internal components utilized to form a variable inductance magnetic flux switch within apparatus10. Referring toFIG. 1, energy harvesting apparatus10is shown as comprising a plunger12to which an external actuation force F can be applied, and a housing14that encases the remaining components of the apparatus as will be discussed in detail below. Plunger12includes a cylindrical base element16and a plate18positioned above base element16as shown. Plunger12is configured to move up and down in a central opening of housing14in a manner such that the application of an external force to plunger12causes it be pressed downward into housing14. As discussed in detail below, plunger12supplies a spring-loaded mechanical force, which is thereafter overcome such that plunger12is moved by spring action back in the opposite direction out of housing14. It is this latter movement of plunger12that induces the flow of electrical current, which exits housing14as shown and is collected by an external electrical energy storage device20(which may comprise a capacitor or other suitable means). Plunger12is pressed downward time and again, with each action of its movement inducing the flow of electricity through an included coil.

FIG. 2presents a cross-sectional view of apparatus10, showing both plunger12and housing14, as well as a mechanical spring22and a variable inductance magnetic flux switch24(hereinafter referred to as “flux switch24” for the sake of brevity).FIG. 3is an exploded view of various components within apparatus10, where it is useful to refer to bothFIGS. 2 and 3for an understanding of the method of providing energy harvesting by apparatus10. In general and in accordance with the principles of the present invention, energy harvesting occurs through the action of flux switch24to convert the movement of mechanical spring22into electrical energy that may be stored (using storage device20as shown inFIG. 1, for example) and thereafter accessed as needed.

Referring to bothFIGS. 2 and 3, mechanical spring22is shown as disposed within housing14so as encircle an inner periphery14-iof the exterior wall of housing14and allow the interior portion of the assembly to remain vacant for the subsequent location of the various components of flux switch24. The particular embodiment of the present invention shown inFIGS. 2 and 3utilizes a “magnetic lock” to control the release of mechanical spring22. An interior wall segment15(concentric with housing14) is included in this embodiment and used as an element of this magnetic lock action (as will be described in more detail below in association withFIGS. 6 and 7).

Continuing with reference toFIGS. 2 and 3, flux switch24itself is shown as comprising a cylindrical ferromagnetic shell26formed to include a centrally-located magnetic core28(which comprises a permanent magnet component). Shell26also includes a trench30located in proximity to its outer wall, where trench30is sized to accommodate the remaining components of magnetic flux switch24in a manner where these components may be moved up and down within trench30of shell26, under the control of the movement of spring22, as described below.

The remaining components of magnetic flux switch24comprise a movable subassembly31, including an electrical coil32that is disposed between a pair of ferromagnetic rings34,36. It is this subassembly31that is positioned within trench30and is able to move up and down along trench30(as mechanical spring22moves, described below). A ferromagnetic lock plate38and a plurality of vertical attachment pins39comprise the physical support for coil32and rings34,36, and terminates as a circular ferromagnetic disk that is attracted to (and thus capable of being dis-engaged from) shell26. As best shown inFIG. 2, lock plate38extends outward toward the periphery of housing14so as to at least cover mechanical spring22. The downward movement of lock plate38(via attached plunger12) thus functions to compress mechanical spring28into the space between housing14and interior wall segment15.

In accordance with this particular embodiment of the present invention, the magnetic attachment between lock plate38and shell26forms the magnetic lock mechanism. As will be discussed below, the contact between lock plate38and interior side wall15functions to dis-engage lock plate38from shell26such that the compressed mechanical spring22is “unlocked” and permitted to return to its de-compressed state.

Also shown inFIG. 2is a return spring40, disposed within a central area of housing14below shell26. As will be discussed below, return spring40(or a similar mechanism) is utilized in accordance with the present invention to re-set the position of plunger12to extend above housing14at the end of an energy conversion cycle so that plunger12is automatically in position to begin the next cycle of the harvesting of mechanical energy.

FIGS. 4-9schematically illustrate the operation of this exemplary embodiment of the inventive apparatus for converting mechanical energy into electrical energy. The apparatus is shown in five stages of operation, as follows:FIG. 4illustrates apparatus10in a “ready” for actuation state (i.e., prior to the application of an external force to plunger12);FIG. 5illustrates apparatus10in a “mechanical force” generation state (i.e., the application of an external force to plunger12to compress spring22);FIG. 6illustrates apparatus10in a “fully compressed” spring state, at a point in time where spring22is first unlocked;FIG. 7illustrates an initial release state (i.e., with mechanical spring22starting to return to its initial state, also moving subassembly31upward within trench30of shell26and away from magnetic core28);FIG. 8illustrates a fully released state; andFIG. 9illustrates a final step of the removal of the external force, allowing return spring40to move plunger12back to its initial position. The details of each state of operation, particularly as it impacts the change in magnetic flux captured by coil32will now be discussed in detail below.

Referring initially toFIG. 4, apparatus10is shown in this initial state with no external force applied to plunger12. Shown in this view is the direction of the magnetic field through magnetic core28, with the flux lines circling as shown around electrical coil32. The captured flux remains constant as long as no external force is applied, and spring22remains fully expanded in its location between housing14and lock plate38. In this initial state, electrical coil32is defined as exhibiting both a maximum flux and a maximum inductance. Since a substantial portion of the total magnetic flux flows through plunger12, this allows for plunger12to be strongly attracted to shell26. This attraction enables the magnetic lock action, as mentioned above, which keeps plunger12attached to shell26.

FIG. 5illustrates a next step in the inventive method of harvesting electrical energy from mechanical energy. As shown, an external force F is applied to plunger12, which begins to compress spring22so that it begins to accumulate mechanical energy. At this point, lock plate38is still engaged with shell26(via the magnetic attraction between the two elements). As long as plate38and shell26remain joined, there is no relative movement between coil32and magnetic core28and, therefore, no change in the flux captured by coil32. Thus, at this point in the process, there is not yet any creation of electrical energy, only the continued accumulation of mechanical energy.

FIG. 6illustrates the point in the process where mechanical spring22is fully compressed in the space between the outer portion of housing14and interior wall segment15with lock plate38still preventing the release of mechanical spring22. As shown, under the continued application of an external force, lock plate38now comes into connect with a top surface of interior wall segment15, which functions as a mechanical “stop” and presents any further downward movement of plate38. Therefore, since an external force continues to be applied to plunger12, at some point in time this force will overcome the magnetic attraction between plate38and shell26, causing shell26to break contact and continue to move downward. The separation of lock plate38from shell26functions to “open” the magnetic lock, releasing fully-compressed mechanical spring22. As shown below, the unlocking allows for subassembly31(consisting of of coil32, plugs34,36, plate38and vertical attachment pins39) to also be moved upward within trench30of shell26by the force of mechanical spring22.

FIG. 7is a simplified diagram of flux switch24at the point in time when lock plate38begins to move upwards under the control of the motion of mechanical spring22. Inasmuch as lock plate38is a component of movable subassembly31including coil32, the upward movement of lock plate38also causes coil32to move upward and thus begin to shift its position with respect to stationary magnetic core28. The change in position between these two elements thus creates a change in the magnetic flux captured by coil32, inducing a flow of current through coil32. The induced current will continue to be created as along as the flux density associated with coil32continues to change (i.e., as coil32and magnetic core28continue to separate by the upward movement of coil32). Thus, in accordance with the teachings of the present invention, the unlocking of compressed mechanical spring22initiates the process of converting mechanical energy to electrical energy, the spring force moving coil32with respect to magnetic core28to induce a current to flow through coil32.

In embodiments where flux switch24is configured to have a range of motion sufficient to allow coil32to be fully lifted out of shell26, there will no longer be any magnetic flux that is captured by coil32once is it fully separated from shell26and away from its magnetic field. It is at this point in time that the coil inductance also drops to its lowest value (since it is no longer embedded within shell26). As mentioned above, this abrupt decrease in coil inductance also generates the flow of electrical current through coil32.

In particular, current will continue to flow until lock plate38comes into contact with plunger12(which is still under force), as shown inFIG. 8. As long as an external force remains applied to this configuration, flux switch24remains stable, with no relative movement between coil32and magnetic core28and, therefore, no further generation of electrical energy.

At some point in time, the external force is removed and return spring40is able to release, as shown inFIG. 9, returning plunger12and attached shell26(including associated magnetic core28) to the initial position. As shell26transitions from the arrangement ofFIG. 8to that ofFIG. 9, an additional current is generated as the flux again goes through another change. However, in this direction the coil inductance is working against the direction of flow of the induced current, so a smaller magnitude of current is created. Apparatus may remain in this state indefinitely, yet ready to begin the next harvesting cycle as soon as an external force is re-applied to plunger12. The ability to remain in the state as shown inFIG. 9is an advantage of the inventive apparatus when used to harvest aperiodic forces.

Summarizing, with electrical coil32and ferromagnetic plugs34,36forming a subassembly disposed to move up and down within trench30of shell26, the achievable separation between electrical coil32and magnetic core28controls how much energy is generated. In configurations where coil32is able to be completely displaced from shell26, a maximum amount of energy is generated.

While optimum in terms of generating maximum electrical energy, the requirement of providing full separation between coil32and shell26is difficult to obtain in manufacture. Thus, other configurations of this embodiment may be preferred where the movement of coil32is somewhat limited (e.g., coil32does not complete exit shell26). Additionally, it is possible to remove switch plugs34,36from the configuration to simply the fabrication process. The elimination of plugs34,36, however, makes the change in captured flux much less abrupt and, as a result, significantly less electrical energy is generated in this arrangement.

Electrical energy generation in accordance with the present invention is actually associated with two different mechanisms. The first mechanism is the change in magnetic flux captured by coil32, as discussed above. The faster coil32moves with respect to magnetic core28, the more electrical energy is generated. The second mechanism by which electrical energy is generated is the related decrease in the inductance of coil32itself when it is energized, as mentioned above. Again, the faster the decrease, the more energy that is generated. However, as noted above this latter component works against energy generation during the “return” trip from the position ofFIG. 8to that ofFIG. 9. While there is still a change in magnetic flux that induces a current, the coil inductance is actually increasing as a result in the change of sign, thus working against energy generation.

Since these final steps of re-setting plunger12constrains the amount of energy that may be generated, the embodiment of the present invention discussed thus far may not be particularly well-suited to support energy generation in systems where oscillatory motion of a mechanical component (spring) is available and useful for energy harvesting. That is, if all of the available mechanical energy cannot be converted to electrical energy during a single cycle of movement through the states shown inFIGS. 4-9, the unused mechanical energy (i.e., the additional oscillations of spring22) will be dissipated as heat.

FIG. 10illustrates another embodiment of the present invention, referred to as a “dual-core” energy harvesting apparatus100. Here, a pair of oppositely-poled first and second magnetic core elements110,112is disposed within a shell114and positioned such that there is an intermediate portion of the ferromagnetic material of shell114separating first magnetic core110from second magnetic core112. As with the single-core embodiment discussed above, shell114includes a trench116, with a movable subassembly117comprising at least an electrical coil118positioned within trench116.

In this particular configuration, an external force is applied to a lock cap120(similar to plunger12, discussed above) to provide the compression of an included mechanical spring, and then the unlocking of this spring force to operate the included flux switch. As best shown inFIG. 11, locking cap120includes a set of pusher arms122that extend downward toward the location of the mechanical spring apparatus portion111of apparatus100. Pusher arms122engage with a compression framework124surrounding an included mechanical spring126, so that the application of an external force to locking cap120is directed through pusher arms122and compression framework124to compress mechanical spring126. As will be discussed below in association withFIGS. 22-24, a mechanical lock configuration is used in this embodiment (instead of a magnetic lock as described above) to control the release of compressed mechanical spring126.

A dual-core embodiment of the inventive energy harvesting apparatus offers several advantages over the above-described single-core embodiment. In particular, the use of the pair of cores110,112allows for various types of bi-directional motion of the movable subassembly, including oscillations around an equilibrium point. As mentioned above, energy generation through oscillatory motion of coil118may be desirable in cases where all of the mechanical energy cannot be converted to electrical energy in a single cycle.

FIGS. 12-20are simplified diagrams showing the evolution of induced current flow through both first magnetic core110and second magnetic core112in accordance with dual-core apparatus100ofFIG. 10. For the sake of simplicity, only the movement of coil subassembly117with respect to the dual-core configuration is shown inFIGS. 12-20, which illustrate the changes in captured flux as coil118moves across each core in sequence. The initial state of the flux switch is shown inFIG. 12, where movable subassembly is positioned above shell114such that coil118is completely withdrawn. Thus, none of the magnetic flux is captured by coil118, as indicated by the magnetic field lines circling through ferromagnetic shell114, magnetic core110and ferromagnetic plug134.

FIG. 13shows a following step where coil118moves downward toward first magnetic core110and begins to capture a portion of its magnetic flux. This change in captured flux thus initiates the flow of an induced current through coil118. The captured flux density continues to increase as coil118moves further downward into alignment with first magnetic core110, as shown inFIG. 14. The continuing change in flux density thus maintains the circulation of the induced current within coil118.

As coil118continues to move downward and away from first magnetic core110, the flux captured by coil118starts to decrease, as indicated by the diagram inFIG. 15. Depending on the spacing between first magnetic core110and second magnetic core112, there may be a point in the cycle where coil118no longer in position to interact with the flux created by either core. Following, as soon as coil118begins to interact with second magnetic core112, the direction of the flux switches as shown inFIG. 16, where this abrupt change causes a spike in the induced electrical current. In similar fashion, as coil118continues its relative motion with respect to second magnetic core112, the amount of captured flux will continue to change, and the induced current will continue to flow within coil118, as depicted in the diagrams ofFIGS. 17-20.

As with the single-core embodiment, there are several different configurations of the dual-core embodiment that may be utilized to simplify its design, albeit at a cost of reduced energy generation. One exemplary embodiment in shown inFIG. 21, where magnetic switch plugs120,122are permanently fixed within the terminations of trench116in shell114.

As mentioned above, the particular dual-core embodiment as shown inFIGS. 10 and 11also illustrates the utilization of a mechanical “lock” configuration to control the release of mechanical spring126and initiate the movement of coil118with respect to first and second magnetic cores110,112. In this particular mechanical arrangement, as shown inFIGS. 22-24, a pair of lock pins200is formed on shell114(only one lock pin200being visible in the view ofFIG. 22). Lock cap120is formed to include a pair of keying arrangements212that engage with the pair of lock pins200. Compression frame124is shown as including pusher pins214that engage with pusher arms122in the manner shown inFIG. 22.

As an external force is applied to lock cap120, its downward movement also causes attached pusher arms122to move downward as well. The engagement between pusher arms122and compression frame124function to transfer this applied force to mechanical spring126, accumulating mechanical energy as the force is continued to be applied.

Indeed, as the application of an external force continues, the movement of lock pins200in keying arrangements212causes the rotation of lock cap120, as shown inFIG. 24. The rotation of lock cap120disengages pusher pins214from pusher arms122, thus “unlocking” the compressed mechanical spring and initiating the relative movement of coil118with respect to first and second magnetic cores110,112.

It is to be understood that this particular mechanical lock configuration is exemplary only, as is the magnetic lock configuration discussed above. Various other mechanisms may be used to control the compression and release of the mechanical spring within the apparatus of the present invention, and all are considered to fall within the scope of the invention as long as the mechanism allows for the movement of the spring to be translated into a movement of the electrical coil so as to create a change in the magnetic flux captured by the coil.

In some cases, the required mechanical displacement may be too large to be captured by either the single-core or dual-core embodiments described above. Thus, another embodiment of the present invention takes the form of a “multi-core” configuration, which consists of a plurality of dual-core units that are disposed in a linear array.FIG. 25illustrates this concept, showing the movement of an exemplary coil300downward through a group of five dual-core units310.

As mentioned above, the variable inductance magnetic flux switch energy harvester of the present invention is particularly suitable for use in situations where an applied force may be aperiodic. The movement of prosthetic lower limbs, as well as orthotic devices coupled to limbs, are exemplary situations where the obviously aperiodic type of human locomotive force applied to these prosthetic/orthotic devices is considered to be a good source of mechanical energy for harvesting in accordance with the principles of the present invention.FIGS. 26-30illustrate various arrangements where a harvesting element of the present invention (for the sake of simplicity, shown in each illustration as a dual-core apparatus100) may be utilized with a prosthetic limb. In general, it is to be understood that the movement of any type of prosthetic or orthotic device may be used to control the energy harvesting capability of an embodiment of the inventive apparatus that is co-located with the prosthetic or orthotic device.

FIG. 26illustrates an exemplary embodiment400where dual-core mechanical energy harvesting apparatus100is utilized in conjunction with a separate prosthetic foot device410. In this embodiment, energy harvesting apparatus100is activated by the movement of prosthetic foot device410. The inclusion of energy harvesting apparatus100functions to accept downward-directed and/or upward-directed and/or rotational forces in the ankle area directly above foot device410and allows that force to be harvested as electrical energy in the manner described above. The harvested electrical energy may be used as a power source for electronic circuitry embedded within prosthetic foot device410, for example.

FIG. 27shows an alternative embodiment420, where dual-core mechanical energy harvesting device100is positioned underneath a prosthetic lower limb430. As with embodiment400ofFIG. 26, energy harvesting apparatus100is activated in this case by the movement of prosthetic lower limb430. In this exemplary embodiment420, energy harvesting device100is oriented such that downward-directed and/or upward-directed and/or rotational forces against the lower termination432of limb430initiates compression of the mechanical spring within apparatus100to being an energy harvesting cycle, as described above.FIG. 28illustrates an embodiment440that comprises a combination of the configurations ofFIGS. 26 and 27, where energy harvesting apparatus100is positioned between prosthetic foot device410and prosthetic lower limb430. In this particular embodiment440, energy harvesting device100is configured to convert mechanical energy associated with downward-directed and/or upward-directed and/or rotational forces into electrical energy.

FIGS. 29 and 30illustrate some alternative embodiments of utilizing the inventive energy harvesting apparatus in combination with prosthetic devices. In this case, the exemplary dual-core mechanical energy harvesting device is directly incorporated within, and forms part of, the prosthetic/orthotic device itself.FIG. 29illustrates an embodiment450where dual-core energy harvesting apparatus100is integrated within an exemplary prosthetic foot device410A.FIG. 30illustrates an embodiment460where dual-core energy harvesting apparatus100is disposed within a knee region434of an exemplary prosthetic lower limb430A. Similar to the embodiments ofFIGS. 26-28, the configurations shown inFIGS. 29 and 30may utilize the harvested energy to power included electronics within the prosthetic devices. Again, it is to be understood that the inventive energy harvesting apparatus may be used to harvest electrical energy from the movement of orthotic devices, as well as prosthetic devices as illustrated in the above examples.

Summarizing, the present invention is directed to an apparatus and method for using the apparatus to provide mechanical-to-electrical energy conversion suitable in a wide range of environments, providing effective coupling to a broad range of forces and displacements that are often not accessible by conventional energy harvesting configurations that rely on high frequency, large amplitude mechanical motion as the mechanical energy source. To achieve the mechanical-to-electrical conversion in accordance with the principles of the present invention, a mechanical energy storage device in the form of a mechanical spring is combined with a variable inductance magnetic flux switch, where the activation of the spring causes a rapid change in the magnetic flux penetrating the electrical coil within the switch. Various embodiments may utilize a single magnetic core, a dual-core arrangement, or even a multi-core arrangement to provide a longer range of motion for the movement of the mechanical spring.

Indeed, useful amounts of power are expected to be generated using various embodiments of the present invention.FIG. 31is a plot of computed results for power generated by the single-core embodiment of the present invention as shown inFIGS. 1-9. Plot A inFIG. 31shows the total power generated by coil32(over hundreds of watts), with the eddy current losses associated with shell26shown in plot B.FIG. 32shows similar plots for the dual-core embodiment, where the pair of peaks in the generated power are expected as the coil achieves maximum change in flux at two separate points in time as it passes by each of the magnetic cores.

The present invention, which is disclosed herein, is not to be limited by the embodiments described or illustrated herein, which are given by way of example and not of limitation. Other embodiments of the present invention will be apparent to those skilled in the art from a consideration of the instant disclosure, or form practice of the present invention. Various omissions, modifications, and changes to the principles disclosed herein may be made by one skilled in the art without departing from the true scope and spirit of the present invention, which is indicated by the following claims.