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Design of Kinetic-Energy Harvesting Floors^{ †}

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## Abstract

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^{®}/Simulink to predict the energy performances of Genpath and help fine-tune the design parameters. The system in Genpath comprises two main parts: the EM generator and the Power Management and Storage (PMS) circuit. For the EM generator, the conversion mechanism for linear translation to rotation was designed by using the rack-pinion and lead-screw mechanism. Based on the simulation analysis, the averaged energy of the lead-screw model is greater than that of the rack-pinion model. Thus, prototype-II of Genpath with 12-V-DC generator, lead-screw mechanism was recently built. It shows better performance when compared to the previous prototype-I of Genpath with 24-V-DC-generator, rack-pinion mechanism. Both prototypes have an allowable displacement of 15 mm. The Genpath prototype-II produces an average energy of up to 702 mJ (or average power of 520 mW) per footstep. The energy provided by Genpath prototype-II is increased by approximately 184% when compared to that of the prototype-I. The efficiency of the EM-generator system is ~26% based on the 2-W power generation from the heel strike of a human’s walk in one step. Then, the PMS circuit was developed to harvest energy into the batteries and to supply the other part to specific loads. The experiment showed that the designed PMS circuit has the overall efficiency of 74.72%. The benefit of the design system is for a lot of applications, such as a wireless sensor and Internet of Thing applications.

## 1. Introduction

^{®}/Simulink for predicting the energy performances of the VEH floors and fine-tuning the design parameters. The entire system consists of two main parts of (1) the EM generator, including the translation-to-rotation conversion mechanism, and (2) the Power Management and Storage (PMS) circuit. For simplicity, a direct-current (DC) generator was used in the design to produce electricity. The rack-pinion and lead-screw mechanisms were adopted to converse a linear motion from a human’s pedal to a rotation of the generator’s rotor. The PMS circuit with extra low energy consumption was designed to simultaneously convert and store electrical energy. The paper is organized into the following sections. In Section 2, the design of each sub-system is described in detail. Then, the installation and demonstration of application are presented in Section 3. Finally, the conclusion is stated in Section 4.

## 2. Design of Subsystems

#### 2.1. The System of EM Generator

#### 2.1.1. Conceptual Design

^{3}with the maximum allowable displacement of 15–20 mm. Two types of mechanisms, rack pinion and lead screw, are used to convert the translation from a footstep to the rotation of the generator. For the rack-pinion mechanism in Figure 2a, the pinion connected to the floor-tile drives the DC-generator shaft through the additional pinion gears which help transform low-speed power to high-speed power. For the lead-screw mechanism in Figure 2b, the nut fixed to the floor-tile’s center moves up and down and drives the lead screw to rotate about its axis. The set of bevel gears transmits the rotation from the lead screw to the DC generator and changes the direction of rotation by 90°. The rotation of the DC generator in both designs then induces the voltage. The springs with the maximum displacement of 15–20 mm connected to the four corners of the block help restore the top floor-tile back to the equilibrium position. Considering the limits of the dimension and the displacement, thus, the small size of 12/24-V-DC motor was decided for the DC generator.

#### 2.1.2. Analysis

^{®}/Simulink. Figure 3a,b show the physical models corresponding to the two systems in Figure 2a,b, respectively. In Figure 3a, the system consists of the elements of rack, pinion and gear on the mechanical side, and the DC generator (with its own resistance, ${R}_{G}$, and inductance, $L$) connected to the load ${R}_{L}$ on the electrical side. Contrastively, the elements of rack, pinion and gear are replaced by the nut, lead screw, and bevel gears for the system in Figure 3b. The footstep force $F\left(t\right)$ is modeled as the arbitrary function reported in [9] and presented in Figure 4. The spring with a maximum compression of 15–20 mm provides the restoring force ${F}_{s}$ to restore the floor-tile back to the equilibrium position. The dynamic equations governing the electro-mechanical models of both designs are formulated as follows.

_{1}and J

_{G}, respectively. By combining (2) and (11)–(12), the equations governing the electro-mechanical system with the lead and screw design are obtained as

^{®}/Simulink models corresponding to (7) and (14) were developed to predict the voltages and currents for various load resistance ${R}_{L}$ that both the EM generator systems with rack pinion and lead screw could generate. The Simulink model of the system with lead screw is presented in Figure 7. With the selected parameters shown in Table 1 and Table 2, the simulation results were compared to the corresponding test results as illustrated in Figure 8 and Figure 9 (The test procedure will be described in Section 2.1.4.). Figure 8 and Figure 9 show that the analytical models accurately predict the magnitudes of the voltages and currents generated by the EM generator. The voltage and current signals in Figure 8 and Figure 9 can be divided into two stages according to the movement, i.e., forward and return stages. In the forward stage, ~0.2–0.8 s, the floor-tile moves downwards when the footstep-force applied, causing the generator to rotate in one direction and hence induce negative voltage and current as shown in Figure 8 and Figure 9. During 0.2–0.8 s, the floor-tile might reach the lowest position, causing the generator to stop the rotation and induce no voltage and current before the return stage begins. In the return stage, ~0.8–1.4 s, the floor-tile moves upwards to the equilibrium position according to the restoring spring forces and drives the generator to rotate backward and induce positive voltage and current as seen in Figure 8 and Figure 9. Note that in Figure 9, there exists the small humps of the predicted voltage and current during 0.6–0.8 s. These signals correspond to the applied force at the same interval when the floor-tile is moving downwards. The discrepancy of this analytical prediction and the test result might be because of the difference between the actual force and the force function in Figure 4.

#### 2.1.3. Design of Elements

#### 2.1.4. Development of the Prototypes

_{L}to provide the maximum power output. Then the voltage across R

_{L}, the current i and the corresponding electrical power when a normal footstep is applied were measured using an oscilloscope and a current probe. The test results are shown in Figure 16 and summarized in Table 8. Genpath prototype-II with 12-V-DC generator and lead-screw mechanism was significantly improved when compared to the prototype-I [16]. It stated in Table 8 that the latest Genpath prototype produces an average energy of 702 mJ (or average power of 520 mW), the maximum voltage of 9.5 V and the maximum current of 285 mA per footstep in the duration of 1.35 s. The energy provided by the EM-generator in Genpath’s prototype-II was increased by approximately 184% when compared to that of the prototype-I [16]. The efficiency of the EM-generator system is 26% based on the power generation from the heel strike of a human’s walk of 2 W per step. This amount of energy could sufficiently power typical low-power electrical devices, as previously described.

#### 2.2. The system of Power Management and Storage Circuit

## 3. Installation and Demonstration

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 8.**Voltage and Current of Rack-Pinion Model from Experiment and Simulation. (

**a**) Voltage of Rack-Pinion Model. (

**b**) Current of Rack-Pinion Model.

**Figure 9.**Voltage and Current of Lead-Screw Model from Experiment and Simulation. (

**a**) Voltage of Lead-Screw Model. (

**b**) Current of Lead-Screw Model.

**Figure 10.**Simulation of Rack-Pinion and Lead-Screw Model. (

**a**) Voltage of Rack-Pinion and Lead-Screw Model. (

**b**) Current of Rack-Pinion and Lead-Screw Model.

**Figure 11.**Simulation of Lead-Screw Model with Soft and Hard Springs. (

**a**) Voltage of Lead-Screw Model with Soft and Hard Springs. (

**b**) Current of Lead-Screw Model with Soft and Hard Springs.

**Figure 12.**Comparison Voltage and Current of Lead-Screw Model with 12– and 24–V-DC Generator. (

**a**) Voltage of Lead-Screw Model. (

**b**) Current of Lead-Screw Model.

**Figure 16.**Comparison Voltage and Current of Prototype I and Prototype II. (

**a**) Voltage of Prototype I and Prototype II. (

**b**) Current of Prototype I and Prototype II.

**Figure 19.**Experimental result showing the operation of power management and storage circuit; ${v}_{t}$ and ${i}_{t}$ are outputs of generator; ${v}_{i}$ and ${i}_{i}$ are outputs of the rectifier circuit; ${v}_{o}$ and ${i}_{o}$ are outputs of the buck-boost circuit.

**Figure 20.**Experimental result showing the operation of the power management system regarding the process of power conversion and energy storage; ${P}_{t}$ and ${E}_{t}$ are power and energy outputs of the generator; ${P}_{i}$ is power output of the rectifier circuit; ${P}_{o}$ and ${E}_{o}$ are power and energy outputs of the buck-boost circuit.

Parameters | Value |
---|---|

Mass of Rack and Plate ($m$) | 3.016 $\mathrm{kg}$ |

Radius of Pinion (${r}_{1}$) | 0.72 × 10^{−2} m |

Radius of Gear (${r}_{2}$) | 3 × 10^{−2} m |

Moment of inertia of bevel gear (${J}_{G}$) | 8.6756 × 10^{−7} |

Moment of Inertia of Pinion (${J}_{p}$) | 1 × 10^{−5} kg m |

Spring Coefficient ($k$) | 20,500 N/m |

Damping Coefficient ($d$) | 900 N·s/m |

Resistance of Generator (${R}_{G}$) | 42 Ohm |

Inductance ($L$) | 19.6 × 10^{−3} H |

Generator constant (${K}_{t}$) | 0.5854 Vs/rad |

Resistance of Load (${R}_{L}$) | 30 Ohm |

Parameters | Value |
---|---|

Pitch of Lead Screw ($l$) | 8 $\mathrm{mm}$ |

Mass of Nut and Plate ($m$) | 2.16 $\mathrm{kg}$ |

Moment of inertia of bevel gear (${J}_{G}$) | 8.6756 × 10^{−7} |

Moment of Inertia of lead screw (${J}_{l}$) | 2.5536 × 10^{−6} kg m^{2} |

Lead angle | 45 degree |

Spring Coefficient ($k$) | 40,000 N/m |

Damping Coefficient ($d$) | 13,600 N·s/m |

Resistance of Generator (${R}_{G}$) | 37 Ohm |

Inductance ($L$) | 19.6 × 10^{−3} H |

Generator constant (${K}_{t}$) | 0.392 Vs/rad |

Resistance of Load (${R}_{L}$) | 30 Ohm |

Friction coefficient (µ) | 0.21 |

Efficient of thrust bearing ${\eta}_{thrust}$ | 0.6529 |

Efficient of thread ${\eta}_{thread}$ | 0.8132 |

Variables | Rack-Pinion Design | Lead-Screw Design |
---|---|---|

Values per Footstep | Values per Footstep | |

Maximum voltage | 9.92 V | 10.13 V |

Average voltage | 0.99 V | 4.16 V |

Maximum current | 330.9 mA | 337.9 mA |

Average current | 33.15 mA | 138.8 mA |

Maximum power | 3.28 W | 3.42 W |

Average power | 216.4 mW | 590.3 mW |

Wave duration | 1.00 s | 1.50 s |

Average energy | 216.4 mJ | 885.8 mJ |

**Table 4.**Comparison of Rach-Pinion, Lead-Screw (60° lead angles) and Lead-Screw (45° lead angles) Average Energy.

Design | Averaged Energy (mJ) |
---|---|

Rack pinion | 319 |

60° lead angles Lead screw | 353 |

45° lead angles Lead screw | 488 |

Voltage (V) | Resistance RG (Ω) | Inductance L (mH) | Kt (Vs/rad) |
---|---|---|---|

12 | 37 | 3.6 | 0.2903 |

24 | 42 | 19.6 | 0.5854 |

Load (Ω) | Average Energy (mJ) | |
---|---|---|

12 V | 24 V | |

30 | 798.2 | 321.5 |

39 | 750.0 | 313.2 |

49 | 745.5 | 488.2 |

Prototype I (Rack and Pinion) | Prototype II (Lead Screw) | ||||
---|---|---|---|---|---|

Item | Dimensions | # | Item | Dimensions | # |

Acrylic plate | 400 × 400 × 10 mm | 2 | Wood plate | 400 × 400 × 5 mm | 2 |

Linear guide | Dia 12 Length 90 mm | 4 | Linear guide | Dia 12 Length 90 mm | 4 |

Linear bearing | Inner dia 12 mm | 4 | Linear bearing | Inner dia 12 mm | 4 |

Shaft coupling | Inner dia 12 mm | 4 | Shaft coupling | Inner dia 12 mm | 4 |

Coil spring | Length 60 mm Dia 1.6 mm | 4 | Coil spring | Length 60 mm Dia 2.2 mm | 4 |

Shaft to generator | Dia 8 mm Length 60 mm | 1 | Shaft to generator | Dia 8 mm Length 60 mm | 1 |

Rack and pinion | Pinion radius 3 cm | 1 | Nut and lead screw | Dia 8 mm Pitch 2 mm | 1 |

Flexible coupling | 8 mm | 1 | Flexible coupling | 8 mm | 1 |

Gear | Radius 0.75 cm | 1 | Bevel gear | Inner dia 8 mm | 2 |

Ball bearing | Inner dia 8 mm | 3 | Ball bearing | Inner dia 8 mm | 3 |

Generator | ZGA37RG 24V 300 rpm | 1 | Generator | ZGA37RG 12V 300 rpm | 1 |

Variables | Prototype I (Rack-Pinion) | Prototype II (Lead-Screw) |
---|---|---|

Values per Footstep | Values per Footstep | |

Maximum voltage | 7.5 V | 9.5 V |

Average voltage | 1.26 V | 2.88 V |

Maximum current | 246 mA | 285 mA |

Average current | 42.5 mA | 88 mA |

Maximum power | 1.85 W | 2.71 W |

Average power | 216 mW | 520 mW |

Wave duration | 1.14 s | 1.35 s |

Average energy | 247 mJ | 702 mJ |

**Table 9.**Performances of power management and storage circuit with Genpath prototypes II and 12-V-DC generator.

Variables | Values per Footstep | |
---|---|---|

Pure $\mathit{R}$ (8.7 Ω) | Power Management and Storage Circuit | |

Maximum voltage; max (${v}_{t}$) | 4.22 V | 3.97 V |

Maximum current; max (${i}_{t}$) | 548 mA | 635 mA |

Maximum power; max (${p}_{t}$) | 2.29 W | 2.48 W |

Average power; ${\overline{p}}_{t}$ | 351 mW | 374 mW |

Average power; ${\overline{p}}_{i}$ | - | 359 mW |

Average power; ${\overline{p}}_{o}$ | - | 280 mW |

Wave duration | 1.18 s | 1.08 s |

Stored energy at 1.4 s; ${E}_{o}$ (t = 1.4 s) | 415 mJ | 302 mJ |

Efficiency of Active Rectifier | - | 95.78% |

Efficiency of Buck-Boost Converter | - | 78.00% |

Overall Efficiency | - | 74.72% |

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**MDPI and ACS Style**

Jintanawan, T.; Phanomchoeng, G.; Suwankawin, S.; Kreepoke, P.; Chetchatree, P.; U-viengchai, C. Design of Kinetic-Energy Harvesting Floors. *Energies* **2020**, *13*, 5419.
https://doi.org/10.3390/en13205419

**AMA Style**

Jintanawan T, Phanomchoeng G, Suwankawin S, Kreepoke P, Chetchatree P, U-viengchai C. Design of Kinetic-Energy Harvesting Floors. *Energies*. 2020; 13(20):5419.
https://doi.org/10.3390/en13205419

**Chicago/Turabian Style**

Jintanawan, Thitima, Gridsada Phanomchoeng, Surapong Suwankawin, Phatsakorn Kreepoke, Pimsalisa Chetchatree, and Chanut U-viengchai. 2020. "Design of Kinetic-Energy Harvesting Floors" *Energies* 13, no. 20: 5419.
https://doi.org/10.3390/en13205419