FOOTWEAR ENERGY HARVESTING APPARATUS AND METHOD
An energy harvesting system for footwear is described having a sole, heel and an upper and comprising a first gaseous bellows pump formed at the sole of the footwear with the bellows hinged forward of the sole; a second gaseous bellows pump formed at the heel of the footwear with the bellows hinged forward of the heel. A gas reservoir is mounted to the upper of the footwear in fluid communication with first and second gaseous pumps downstream of the pumps and adapted to receive the gaseous medium exiting under pressure from the pumps. An axial turbine has an output shaft mounted on the footwear upper downstream of the reservoir and adapted to receive pressurized gas from the reservoir when a predetermined pressure threshold is attained in the reservoir so as to activate the axial turbine; and an electrical generator mounted on the upper, downstream of the axial turbine and engaged with the turbine output shaft which can be engaged only when a predetermined shaft velocity threshold has been attained.
This application claims priority on U.S. Provisional Application No. 61/990,942 filed on May 9, 2014, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTIONThe present invention relates to an apparatus set in footwear for the purpose of generating electricity for the purposes of powering electrical accessories carried by the wearer, and the method therefore.
BACKGROUND ARTThere has been a history of endeavors to harvest energy from footwear in order to produce electrical power for the purpose of energizing various accessories worn by a person, such as to operate “ . . . an electric lamp, a heating coil, a small wireless outfit, a therapeutic appliance . . . ” as described in U.S. Pat. No. 1,506,282 Barbieri in 1924. Since then many attempts have been made as illustrated by Lakic in U.S. Pat. No. 4,674,199 January 1987; U.S. Pat. No. 4,736,530 April 1988; U.S. Pat. No. 4,782,602, November 1988; U.S. Pat. No. 4,845,338 July 1989 and U.S. Pat. No. 4,941,271, July 1990; Chen in U.S. Pat. No. 5,167,082 December 1992; U.S. Pat. No. 5,367,788 November 1994 and 5,495,682 March 1996. More recently there has been Landry U.S. Pat. No. 6,201,314 March 2001; Le et al U.S. Pat. No. 6,255,799 July 2001; Sarich U.S. Pat. No. 6,281,594 August 2001 and Yang U.S. Pat. No. 7,956,476 June 2011. A paper entitled Parasitic Power Harvesting in Shoes by John Kymissis et al, from the MIT Media Laboratory, was presented at the Second IEEE International Conference on Wearable Computing in August, 1998.
With increased use of power-consuming portable electronics, the need for compact and lightweight power sources to replace batteries is becoming more urgent. Harvesting energy from walking such as from the force developed in compressing footwear soles and heels has been shown to generate anywhere from 1 to 7 W cap (continuous average power). However the challenge remains in converting this mechanical energy into useful electricity with miniaturize components.
Accordingly, improvements are desirable.
SUMMARYIt is therefore an aim of the present invention to provide an improved footwear energy harvesting apparatus and related method.
Therefore, in accordance with the present invention, there is provided an energy harvesting system for footwear comprising a first gaseous pump formed at the sole of the footwear and a second gaseous pump formed at the heel of the footwear. A reservoir is mounted to the upper of footwear in fluid communication with and downstream of the first and second pumps and adapted to receive pressurized gas exiting from the pumps. A turbine having an output shaft, is mounted on the footwear upper, in fluid communication with and downstream of the reservoir. The turbine includes an inlet port section for receiving the pressurized gas from the reservoir, when a predetermined pressure threshold is attained in the reservoir, so as to activate the turbine; and an electrical generator mounted on the upper, downstream of the turbine and disengageably connected with the turbine output shaft so that the generator is engaged by the shaft when a predetermined shaft velocity threshold has been attained whereby electricity may be generated in order to energize or be stored by a device worn by the bearer of the footwear.
In another aspect, there is provided a multistage, axial turbine for converting energy from a pressurized gas to mechanical energy which may be used within a footwear energy harvesting system. The turbine includes a casing having an inlet and an outlet at axially aligned opposite ends of the casing, and the casing houses a cylindrical hollow stator and an elongated rotor concentric with the stator. The rotor includes a plurality of stages of radially extending rotor blades spaced circumferentially in each stage, while the stator is provided with rows of radially extending stator vanes circumferentially spaced apart in each row and the rows are located inter-stage of the rotor blade stages. The casing includes a diffuser at the inlet provided to receive the pressurized gas and to direct it to the rotor and stator. The casing is provided with bearings at the inlet and the outlet and the rotor has an upstream shaft and an output shaft coaxial with the upstream shaft and the shafts rotating freely while being supported in the respective bearings.
In yet another aspect there is a method of harvesting energy from footwear comprising the steps of compressing a gas in a chamber at the sole of the footwear transferring the compressed gas to a second chamber at the heel of the footwear; further compressing the gas in the second chamber; transferring the compressed gas from the second chamber to a reservoir; repeating the compression steps until the pressure in the reservoir has reached a threshold level; once the pressure level in the reservoir has reached the threshold level, passing the pressurized gas through a turbine to convert the energy from the pressurized gas to mechanical energy by rotating the turbine rotor and dependent shaft to reach a speed threshold; once the speed threshold of the shaft has been reached, engaging the shaft with an electric generator; storing the electricity and/or driving a device carried by the bearer of the footwear.
Reference will now be made to the accompanying drawings, showing by way of illustration a particular embodiment of the present invention and in which:
Referring now to
Likewise the outsole 14 a pivots about a hinge 22 in the toe region of the boot 10. The outsole 14 can pivot in a vertical plane about an axis at the hinge 22 that is normal to the vertical plane. A flexible, impermeable bellows wall 24 is provided defining a bellows chamber 25 between the boot and the pivoting outsole 14a. A oneway air inlet valve 25a is provided in the bellows wall 24, which otherwise is airtight.
An air conduit 32 communicates the bellows chamber 25 with the bellows chamber 21. A one-way check valve 31 interrupts the conduit 32 to prevent the air from returning into the chamber 25. When a person weighing 180 lbs places weight on the outsole 14a, the air in the relatively large bellows chamber 25 is compressed to 10-l3 psi. The outsole 14a has an area of approximately 10 in2 (65 cm2). The air then passes through conduit 32 to the relatively smaller bellows chamber 21.
When the weight of the user is transferred to the heel 12, the pre-compressed air is now compressed to between 25-30 psi (172 kPa-207 kPa); partly because of the smaller heel area providing a smaller chamber 21.
The compressed air from the bellows chamber 21 passes through the conduit 28 to the reservoir 26, interrupted by a one-way check valve 30. The reservoir 26, mounted on the side of the upper 16 of the boot 10, typically has a capacity of 12 in3 (197 cm3), in order to provide storage capacity for the compressed air before it is released to the turbine 34.
An air conduit 36 communicates the reservoir 26 to the turbine 34. The air conduit 36 is interrupted by a pressure control valve 38. It was determined that the ideal pressure for delivering the air to the turbine 34 is between 30 and 40 psi, but the latter is preferred.
A control panel 40 is mounted to the side of the upper 16 and preferably between inner-layers forming the upper 16. An air-line 42 extends between the valve 38 and a pressure regulator 43 on the control panel 40. The valve 38 is opened by the pressure regulator, when the pressure threshold e.g. 40 psi is attained.
As shown in
The stator 70 is fabricated in semi-cylindrical segments 70a and 70b, forming a sleeve which is mounted within the casing 60 and is concentric with the rotor 68. In certain conditions the stator may be in three segments. As shown in
Returning now to
Reference will now be made to
For a standard axial turbine with a rotor designed in such a way that the exit velocity at all stages is oriented in the axial direction, the ideal specific work per stage (work per unit mass) is given by wt=Ut Vθ1, Ut being the tangential velocity of the rotor at the mid-radius (Rt) and Vθ1 being the tangential velocity of the airflow at the blade leading edge. The energy extracted by a turbine equipped with Vθ1 stages is then (assuming, in this simplified case, that each stage produces the same amount of work):
ET=φ=Δm wtNsηt=Δm UtVθ1Nsηt
The tangential velocity of the airflow:
The tangential velocity of the airflow is a high value but is limited by the speed of sound at standard ambient temperature. It is also limited by the need to keep frictional losses as low as possible.
The mass flow rate is assumed to be constant as the available mass of air stored in the tank 26 discharges very quickly through the turbine 34. The duration of the constant velocity period is very short and what is observed is rather a regime of acceleration followed by a deceleration time.
The radius of the rotor hub is R1 while the rotor tip is R3. The radius of the inner rim of the stator is R4 while the stator vane tip is R2. It has been shown that clearances, defined by the distance between the stator vane tips and the rotor hub R2-R1 and the distance between the rotor blade tips and the stator rim R4-R3, should be kept as small as possible. Thus, the air leakage from one stage to another is minimized. The optimum design was manufactured with clearance R2-R1 of 0.120 mm and clearance R4-R3 of 0.100 mm.
The preferred rotor blade design and stator blade design is shown in
The angle of attack of the rotor blade at the leading and the trailing edge are respectively defined by:
The turbine 36 has been manufactured with α1=86° and β2=35°. The blade height of the rotor varies from 0.692 mm at stage 1 to 1.004 mm at stage 8.
The number of stages should be as low as possible to limit the manufacturing difficulties, but high enough to limit tangential velocity of the air flow. The 8-stage turbine assembly 34 is shown in
Other factors affecting the turbine performamce is the temperature inside the storage tank 26 as well as the pressure and density. There is a pressure drop across each stage as a result of a temperature drop across the stages. To evaluate the pressure drop at each stage, a polytropic expansion is considered. For an ideal gas, the exit pressure at a given stage i is determined by:
The inlet temperature Ti
For a constant axial velocity Ua of the airflow, this results in an increase of the turbine exit flow area Ae
The exit flow area of a given stage can be defined as:
Ae
with the outer and inner radii of stage i respectively noted Rout
Rout
The following expression for ΔRi is:
This determines the small flow area as a result of the small rotor radius parameters added to the high tangential velocity of the air flow and the small available mass of air.
The turbine 34 has been manufactured by rapid prototyping using Multi Jet Modeling technique (MJM 3D printer from 3D Systems). CNC can also be used.
Referring now to
The shaft 66 of the turbine 34 is coupled to the generator 44 only when a shaft speed threshold has been attained e.g. 90,000 rpm. The CPU 88 sends a signal to ON switch 54 in order to engage the shaft 66 to the generator shaft 46. The generator 44 will generate electrical energy which can be stored in battery 90. As shown in
The nature of the pumping process and the need to constantly accelerate and decelerate, the generator shaft 46 causes a pulsing of the electrical current produced by the generator 44. As shown in
- cv=specific heat at constant volume [J/kg K]
- cp=specific heat at constant pressure [J/kg K]
- Ef=energy losses due to friction [J]
- ET=energy extracted by the turbine [J]
- Ia=moment of inertia [kg m2]
- mT=storage tank air mass [kg]
- N=rotational speed [rpm]
- PT=storage tank air pressure [Pa]
- patm=atmospheric air pressure [Pa]
- R=ideal-gas constant for air (R=cp−cv) [J/kg K]
- Tatm=atmospheric air temperature [K]
- TT=storage tank air temperature [K]
- VT=storage tank volume [m3]
- W=work [J]
- {dot over (W)}=power [W]
- φ=exergy (useful energy) [J]
- ρT=storage tank air density [kg/m3]
- ρatm=atmospheric air density [kg/m3]
- ω=angular velocity [rad/s]
Claims
1. A footwear energy harvesting system comprising a first gaseous pump formed at the sole of the footwear; a second gaseous pump formed at the heel of the footwear; a reservoir mounted to the upper of footwear in fluid communication with and downstream of the first and second pumps and adapted to receive pressurized gas exiting from the pumps; a turbine having an output shaft, mounted on the footwear upper, in fluid communication with and downstream of the reservoir; the turbine including an inlet port section for receiving the pressurized gas from the reservoir, when a predetermined pressure threshold is attained, so as to activate the turbine; and an electrical generator mounted on the upper, downstream of the turbine and disengageably connected with the turbine output shaft so that the generator is engaged by the shaft when a predetermined shaft velocity threshold has been attained whereby electricity may be generated in order to energize or be stored by a device worn by the bearer of the footwear.
2. The footwear energy harvesting system as defined in claim 1 wherein the pressurized gas from the first pump is communicated to the second pump to pre-pressurize the gas to the second pump and the second pump communicates the pressurized gas to the reservoir.
3. The footwear energy harvesting system as defined in claim 3 wherein the first gaseous pump formed at the sole of the footwear includes an outersole hinged to the forward part of the sole and includes an impermeable bellows wall defining a first pump chamber, and an inlet one-way valve for allowing air into the first pump chamber; and, the second gaseous pump includes a heel potion hinged to the forward part of the heel and includes an impermeable bellows wall defining a second pump chamber, and an inlet one-way valve for allowing air into the second pump chamber.
4. The footwear energy harvesting system as defined in claim 1 wherein a one way valve is provided in a gas conduit providing fluid communication between the reservoir and the turbine inlet port section, the valve is controlled by a pressure regulator to open and close the valve to control the debit of pressurized gas to the turbine.
5. The footwear energy harvesting system as defined in claim 4 wherein the predetermined pressurized gas threshold is 30 psi (207 kPa).
6. The footwear energy harvesting system as defined in claim 5 wherein the predetermined pressurized gas threshold is 40 psi (276) kPa).
7. The footwear energy harvesting system as defined in claim 1 wherein a rotary speed detector is provided to determine the speed of the turbine output shaft; the speed detector is in communication with an on/off switch means to engage or disengage the generator from the output shaft whereby the generator is engaged only when the output shaft speed is above a predetermined speed threshold.
8. The footwear energy harvesting system as defined in claim 7 wherein the output shaft speed threshold is 90,000 rpm.
9. The footwear energy harvesting system as defined in claim 1 wherein the turbine is a minituarised, multistage axial turbine with concentric rotor and stator.
10. The footwear energy harvesting system as defined in claim 9 wherein the turbine inlet port section includes a diffuser and the rotor includes an input shaft coaxial with the output shaft.
11. The footwear energy harvesting system as defined in claim 10 wherein the turbine includes eight stages.
12. The footwear energy harvesting system as defined in claim 11 wherein the turbine includes a casing with dimensions compatible with being mounted on the upper of a boot.
13. The footwear energy harvesting system as defined in claim 12 wherein the dimensions of the turbine casing that includes an axial length of 51 mm and a diameter of 10 mm.
14. The footwear energy harvesting system as defined in claim 4 wherein the gas is air and first and second bellows pumps have respective air inlets with one way valves.
15. The footwear energy harvesting system as defined in claim 14 wherein the first bellows pump has an outsole that is hinged to the toe portion of the sole and the outsole has an area of approximately 10 in2 (65 cm2) and a person of 180 lbs (82 kg) can compress the air to an exit pressure of 10-13 psi (69 kPa-90 kPa).
16. The footwear energy harvesting system as defined in claim 15 wherein the pre-pressurized air from the first bellows pump enters the second bellows pump and is compressed to 25-30 psi (172 kPa-207 kPa) upon a person shifting its weight to the heel.
17. The footwear energy harvesting system as defined in claim 1 wherein the reservoir has a volume capacity of 12 in3 (197 cm3).
18. A multistage, axial turbine for converting energy from a pressurized gas to mechanical energy; the turbine including a casing having an inlet and an outlet at axially aligned opposite ends of the casing, the casing housing a cylindrical hollow stator and an elongated rotor concentric with the stator; the rotor including a plurality of stages of radially extending rotor blades spaced circumferentially in each stage; the stator provided with rows of radially extending stator vanes circumferentially spaced apart in each row and the rows provided inter-stage of the rotor blade stages; the casing including a diffuser at the inlet provided to receive the pressurized gas and to direct it to the rotor and stator; the casing provided with bearings at the inlet and the outlet and the rotor having an upstream shaft and an output shaft coaxial with the upstream shaft and the shafts rotating freely while supported in the respective bearings.
19. The multistage, axial turbine as defined in claim 18 wherein the turbine is miniaturized for use within a footwear energy harvesting system.
20. The miniaturized, multistage, axial turbine as defined in claim 19 wherein the rotor has 8 stages.
21. The axial turbine as defined in claim 19 where the angle of the leading edge of each stator vane is set at 0° to the axis and the trailing edge is defined by: α 1 = tan - 1 ( V θ 1 U a ).
22. The axial turbine as defined in claim 21 wherein the angle of attack of the rotor blade at the leading edge and the trailing edge are respectively defined by: β 1 = tan - 1 ( V θ 1 - U t U a ) and β 2 = tan - 1 ( U t U a )
23. The axial turbine as defined in claim 22 wherein α1=86° and β2=35°.
24. The axial turbine as defined in claim 22 wherein the turbine has eight stages and the height of the rotor blades increase from 0.692 mm at the upstream stage and 1.004 mm at the downstream 8th stage.
25. A method of harvesting energy from footwear comprising the steps of compressing a gas in a chamber at the sole of the footwear; transferring the compressed gas to a second chamber at the heel of the footwear; further compressing the gas in the second chamber; transferring the compressed gas from the second chamber to a reservoir; repeating the compression steps until the pressure in the reservoir has reached a threshold level; once the pressure level in the reservoir has reached the threshold level, passing the pressurized gas through a turbine to convert the energy from the pressurized gas to mechanical energy by rotating the turbine rotor and dependent shaft to reach a speed threshold; once the speed threshold of the shaft has been reached, engaging the shaft with an electric generator; storing the electricity and/or driving a device carried by the bearer of the footwear.
26. The method as defined in claim 25 wherein the pressure threshold is 40 psi.
27. The method as defined in claim 25 wherein the speed threshold is 90,000 psi.
28. The method as defined in claim 25 wherein the turbine is an axial turbine and the pressurized gas is fed through the inlet of the axial turbine to rotate an elongated rotor that is concentric with a cylindrical stator causing the rotor to rotate at speeds exceeding 100,000 rpm.
29. The method as defined in claim 28 wherein the gas is air.
Type: Application
Filed: May 8, 2015
Publication Date: Nov 12, 2015
Inventors: REGIS FORTIN (LAVAL), JEAN LEMAY (QUEBEC), MICHEL BISSON (BLAINVILLE)
Application Number: 14/707,020