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Design of Kinetic-Energy Harvesting Floors energies Article y Design of Kinetic-Energy Harvesting Floors Thitima Jintanawan 1, Gridsada Phanomchoeng 1,2,*, Surapong Suwankawin 3 , Phatsakorn Kreepoke 1, Pimsalisa Chetchatree 1 and Chanut U-viengchai 3 1 Department of Mechanical Engineering, Chulalongkorn University, Bangkok 10330, Thailand; [email protected] (T.J.); [email protected] (P.K.); [email protected] (P.C.) 2 Smart Mobility Research Unit, Chulalongkorn University, Bangkok 10300, Thailand 3 Department of Electrical Engineering, Chulalongkorn University, Bangkok 10330, Thailand; [email protected] (S.S.); [email protected] (C.U.-v.) * Correspondence: [email protected]; Tel.: +66-2-218-6630 This paper is an extended and revised article presented at the International Conference on Sustainable y Energy and Green Technology 2019 (SEGT 2019) on 11–14 December 2019 in Bangkok, Thailand. Received: 18 September 2020; Accepted: 12 October 2020; Published: 16 October 2020 Abstract: Alternative energy generated from people’s footsteps in a crowded area is sufficient to power smart electronic devices with low consumption. This paper aims to present the development of an energy harvesting floor—called Genpath—using a rotational electromagnetic (EM) technique to generate electricity from human footsteps. The dynamic models of the electro-mechanical systems were developed using MATLAB®/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. Keywords: energy harvesting; electromagnetic generator; energy floor tile; power management system; footstep energy harvesting; piezoelectric; energy harvesting paver 1. Introduction The smart internet of things (IoT) has been brought to the world’s attention lately. The smart IoT-devices, e.g., Radio-frequency identification (RFID) sensor, Global Positioning System (GPS) tracking, etc., are widely used in the crowded areas such as airports and public stations, commercial buildings, and department stores [1,2]. Seeking an alternative energy for such devices, it was noticeable that a large population can generate power from their footsteps, grabbing the authors’ attention. Therefore, the ultimate goal was to develop an affordable Vibration Energy Harvesting (VEH) system—called Genpath—the smart floor capable of conversing kinetic energy from thousands Energies 2020, 13, 5419; doi:10.3390/en13205419 www.mdpi.com/journal/energies Energies 2020, 13, 5419 2 of 19 of footsteps into electrical energy. Genpath can be installed in places with a crowded population for harvesting energy. Energy harvesting from human motions is an interesting and applicable issue, thanks to the ultra-low power consumption of electronic devices lately [3]. Focused on walking, the energy produced by the heel strike of a person’s walk is 1–5 J or 2–20 W per step [4]. There are various commercial products which harvest energy from people’s walks, such as energy storage shoes [5] and the energy floor [6–11]. Pavegen and Energy Floors have produced a commercial system that generates power from footsteps [6,7]. The Pavegen system, using electromagnetic generators, can produce 2 to 4 joules, or around 5 watts of power of off-grid electrical energy per step. The Energy Floors focuses on harvesting energy from humans dancing and playing games. Dutch Railways built a novel phone charger for Utrecht Central Station using a swing set called Play for Power [8]. The system turns kinetic energy from the swings into power dispensed through charging cables. However, few technical details of those products are published thus far. Kinetic energy, among practical energy-harvesting sources, comes in various forms, e.g., seismic noise, vibration of rotating machinery, motions of vehicles and humans, etc. Vibrational energy harvesting (VEH) is the concept of converting kinetic energies present in the environment into electrical energy. There are two main techniques of kinetic-to-electrical energy conversion applicable to the design of the VEH floor: i.e., piezoelectric generators and electromagnetic generators [12]. The piezoelectric generator produces an electrical charge and energy when deformed under mechanical stress. Piezoelectric generators can provide high voltage levels up to several volts. With its compact size, the piezoelectric generator gives high-power density per unit of volume [13]. The electromagnetic (EM) generator generates an electromotive force (EMF) and thus energy when the permanent magnet relatively moves through the coil. Both techniques of VEH discussed are suitable for generating energy for low-power electronic instruments. However, the piezoelectric generator effectively gives out maximum energy at around its natural frequencies, i.e., higher than 200 Hz, whereas the bandwidth of human motion is between 1–10 Hz. In contrast, the electromagnetic generator is effective in the frequency range of 2–20 Hz. Hence, it is more suitable for harvesting energy from human movements. In addition, the electromagnetic generators also yield higher power density and their costs are much lower than the piezoelectric generators [14]. For the piezoelectric generator, it needs a structural design not only to optimize the power density but also to protect the piezo element itself due to its fragility, while the structural design of the EM generator is much simpler for the application of a VEH floor. There are also two types of the EM generator in terms of energy-conversion mechanisms: linear oscillation to electrical energy and rotation to electrical energy [15]. The mechanism of linear oscillation conversion is simpler, but it requires the larger amplitude of excitation to produce electricity, whereas human pedals are random in vibration with low amplitude. Consequently, the rotational EM generator was chosen for the VEH floor to convert kinetic energy from people’s footsteps into electrical energy. The objective of the paper is to design a simple but efficient VEH floor embedded with the rotational electromagnetic (EM) generator. To achieve this purpose, the dynamic models of the electro-mechanical systems were developed using MATLAB®/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 Section2, the design of each sub-system is described in detail. Then, the installation and demonstration of application are presented in Section3. Finally, the conclusion is stated in Section4. Energies 2020, 13, 5419 3 of 19 2.Energies Design 2020 of, 13 Subsystems, x FOR PEER REVIEW 3 of 19 The development of the VEH floor floor—called—called Genpath—capableGenpath—capable of harvesting kinetic energy from people’s footstepsfootsteps and and converting converting it to it electrical to electrical energy energy is presented. is present In theed process. In the of process energy generation,of energy thegeneration, rotational the EM rotational generator EM is deployedgenerator asis deployed it is independent as it is independent from the resonant from frequencythe resonant and frequency achieves higherand achiev energyes higher density energy when compareddensity when to the compared linear EM to generatorsthe linear EM [15]. generators Figure1 shows [15]. Figure the diagram 1 shows of the completediagram of system the complete in Genpath. system In Figurein Genpath.1, when In the Figure force 1, from when a footstepthe force is from applied a footstep on the is floor-tile, applied theon the mechanism floor-tile, for the a mechanism movement-converter for a movement changes-converter the translation changes of thethe floor-tiletranslation to theof the rotation floor- oftile the to EMthe rotation generator of tothe induce EM generato voltage.r Withto induce the connected voltage. With PMS the circuit, connected the electrical PMS circuit, voltage the and electrical power generatedvoltage and by power the EM generated generator by is the processed. EM generator The harvested is processed power. The is harvested then stored power in the is rechargeable then stored batteriesin the rechargeable so it can be suppliedbatteries to so the it smart can be IoT-devices supplied with to the low smart energy IoT consumption.-devices with Two low main energ parts,y i.e.,consumption.
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