Energy Harvesting From Human Locomotion: Gait Analysis, Design and state of art Hesmondjeet Oon Chee Hounga, Siti Sarahb, S.Parasuramanc, M.K.A.Ahamed Khand*, I. Elamvazhuthie a,c
School of Engineering, Monash University Malaysia, Bandar Sunway, 46150 Selaongor, Malaysia.
b,d
Faculty of Engineering, University Selangor,Malaysia. eFaculty of Engineering, University Technology Petronos, Ipoh, Malaysia. b c
[email protected]
[email protected] d
e
[email protected]
[email protected]
Abstract - Human power is defined as the use of human work for energy generation to power an electronic device. The active powering of electronic devices takes place when the user of the electronic product has to do a specific work in order to power the product that otherwise the user would not have done. As fossil fuels around the world depletes, alternate means of harvesting energy is required. Biomechanical energy harvesting–generating electricity from people during daily activities–is a promising alternative to batteries for powering increasingly sophisticated portable devices. Effectively harvesting energy from walking requires a small lightweight device that efficiently converts intermittent, bi-directional, low speed and high torque mechanical power to electricity, and selectively engages power generation .To achieve this, Linear, Piezo electric and rotary electromagnetic
generation methods are implemented on the model to harvest energy from the heel strike. Qualysis Tracking Markers (QTM), insole pressure sensors, and electromyography (EMG) readings are utilized to analyze the human locomotion during a normal human gait cycle. In this methods-focused paper, we explain also the physiological principles that guided our design process and present a detailed description of our device design with an emphasis on new analyses. Index terms: Biomechanical, Qualysis Tracking Marker, Electromyography, Human gait cycle
I
INTRODUCTION
With the increasing number of human in any country, human need and use the energy to do work or more to a place and well-being ever since existed millions years ago. As a result, many resources have been wasted with impurity. So, non-conventional energy is very essential at this time on any nation. Walking is a common activity performed by a person in he or she’s everyday life. When a person is walking, the energy will be reduced due to the weight transfer to the surface of the foot during walking. Therefore, the energy of the person from the foot step can be converted to the electricity energy. Human power is an attractive energy source. Muscle converts food into positive mechanical work with peak efficiency of approximately 25%, comparable to that of internal combustion engines [7]. The work can be performed at a high rate, with 100 W mechanical easily sustainable by an average person [8]. Food, the original source of the metabolic energy required by muscles, is nearly as rich an energy source as gasoline and approximately100 fold greater than batteries of the same weight [9].
1.1. The body as a source of energy – theoretical considerations The idea of harvesting energy from human motion is based on the fact that an average person’s energy expenditure, which is the amount of energy used by the bodies 1.07*107 J per day [18], an amount equivalent to approximately 800 AA (2500 mAh) batteries, whose total weight is about 20 kg. This energy is generated from energy dense sources. In comparison to batteries, this amount of energy can be produced from 0.2 kg of body fat. We note here that human energy is derived from food (carbohydrates, fats, and proteins), and the specific energy of food is typically 35 to 100 times more than the specific energy of currently available batteries (depending on the type of batteries used) [17]. 1.2. Heel strike Heel strike refers to the part of the gait cycle during which the heel of the forward limb makes contact with the ground. Several researchers, e.g., [13], have modeled this motion as a perfect plastic collision, while others believe that there is an elastic component to this motion, e.g., [12, 13]. It is, however, generally agreed that energy is lost during the collision. Researchers predicted that for a typical runner moving at 4.5 m/s, the value of the dissipated energy could range from 1.72 to 10.32 J during a single step and that most of the energy loss would occur during the heel strike. II
ENERGY HARVESTING METHODS
2.1 Piezo electric generator method The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. Applied mechanical force results in internal generation of electrical charge. When the human is walking, jumping or stepping on the plate device which consists of the piezoelectric, the piezoelectric generator will generate electricity from the force created by the human. (Fig.1a) describes the process flow involved in harvesting the energy from Piezo electric sensors with appropriate converters for proper energy utilization.
(b)
(a) )
(b) (a) Figure 1 (a) Block diagram of Piezo electric method of Energy harvesting (b) Regulator and
Boost Converter The piezoelectric sensor output will be connected to a regulator circuit Fig.1(b) to stabilize the voltage to 2.4 volt. 2.2 Regulator Circuit and Boost converter circuit The regulator output voltage 2.4v can be used to charge the battery 2.4 Volts. The boost converter circuit (Fig.1b) is used to boost the voltage between 10 to 12 Volts suitable to charge the rechargeable battery 12 Volts as primary voltage storage. As the step numbers are increased the voltage harvested also tend to increase. The voltage generated is proportional to the human weight as shown in Fig. 2(b).The complete experimental setup is shown in Fig. 2(a), which is built and humans with different weights are subjected on the platform inside which the Piezo disc was kept.
Figure 2 (a) Experimental set up, Figure 2(b) output voltage with respect to different human weight
2.3
Analysis of Human Locomotion
Qualisys Tracking Markers (QTM) were placed on the subject’s lower torso to construct a human model as per the Fig.3.In building a conventional gait model, there are 4 sections mainly pelvis, thighs, shanks and feet are selected for marker placements. The Helen Hayes Pelvis marker set was chosen as a 3 markers set which can be observable by the Qualisys cameras.
Figure 3 Overall Marker Placement of the Subject The focus of the analysis of human gait cycle is the height and angle of the calcaneus just before the heel strike. The subject is asked to walk at different speed on the treadmill – 2kmph, 3kmph and 4kmph to understand the changes in human locomotion with the increase in walking speed. It is seen that the height of the heel from the ground and the angle of the ankle depends greatly on the period of human gait cycle. The minimum height of the heel during mid-swing is found Fig.(4a) to be right before the heel strike that is approximately 15mm, exceeding this height may cause inconvenience to the user. From the plot in Fig.(4b), it is observed that the angle of the ankle during heel strike is approximately 2 degrees. This shows that the angle of the ankle does not affect the device construction.
Height (mm)
Output Voltage (V)
Sensor 1
Insole Sensor 2
Time (s)
Figure (4a) Variation of the angle and height with respect to walking speed
Figure .(4b)Angle
of ankle with respect to time. 2.4
Heel strike impactual force
The main focus for the experiment is to determine the force of impact on the bottom of the heel during a heel strike. The insole pressure sensors were placed at the bottom of the calcaneus and phalanges as shown in
Figure 5 (a) Insole Pressure Sensor and placement (b) Insole Pressure Sensor and placement
Table 1: Voltage Readings from Insole Sensors at Various Speeds Walking Speed Maximum Input Voltage (V) (kmph) Phalange
Calcaneus
2
0.234
0.217
3
0.253
0.217
4
0.267
0.217
Output Voltage (V)
Time (s)
The output voltage as indicated in Fig.5(b) of the insole pressure sensor is then converted to force given that average conversion rate of the sensor is 0.58mV/kPa and the given area is 349mm2. Using the data given above, the equation for obtaining the force during heel impact while walking from the sensors input as shown in equation (1). 𝐹𝑜𝑟𝑐𝑒 =
!"#$%&'(%)*+ !" !.!" !"/!"#
∗
!"#!! !"!
𝑘𝑁
(1)
The calculated heel strike produces an average of 130N on the calcaneus region. It is observed from( Table 1) ,that even though the speed of walking increases, the impact force on the calcaneus during the heel strike does not vary too much from 2kmph to 4kmph. 2.5 Muscle Activities The electrical activities produced by the skeletal muscles are measured using electromyography (EMG).The objective of obtaining the EMG readings is to place a constant so that the difference in muscle activity can be measured when each device is used as a measure of discomfort. The data obtained from the EMG readings as referred by Figure 6 will be kept as a constant as mentioned before. Another reading will be taken once a fully functional mechanism is placed on the subject while walking. The difference between the readings will indicate the percentage
increase in muscle activities to incorporate the mechanism into daily life and suggest the comfort level of the mechanism.
Figure 6.Electromyography Reading Corresponding to the Human Gait Cycle 2.6
Linear Generation Method
Linear generation was considered as the models which have simple designs and can be easily replicated. The device Figure 7(a) was designed based on a linear electromagnetic generator. The
Voltage (V)
Power (W)
device was fabricated using aluminum, which displayed properties required for the device, mainly light and cheap.
Time (s)
Figure 7.
(a) Linear Generating, (b) Output Voltage at Speed of 13.26cm/s
(c) Energy
and power by Linear model at various speeds The linear generator was then tested using the testing platform. The output waveform is recorded using NI ELVIS and plotted as shown in Figure 7(b). As mentioned, the device is tested using 5 different speeds the plot shown is the output waveform using the actuating speed of 13.26cm/s. The peak voltage output ranges from 0.2 V to -0.2Vwhich is insufficient to be passed through the rectifying circuit. Hence, the rectifier circuit was not used to determine the performance of this linear generating model. By measuring the resistance at the coils which is found to be 132Ω, the power generated is calculated using P = V2/R and the results is again plotted as shown in Figure
7(b). The calculated average energy at the speed of 13.26 cm/s is 9.8729e-06J while the maximum power generated is 0.00048666W. Using the 5 different data sets obtained from the experiment, the relationship between the simulation speed and the energy harvested is plotted as shown in Figure 7(c). 2.7 Rotary Generation Rotary design was decided to be too complicated for fabrication in the short period. Therefore, the mechanism as shown in Figure (8) possessing similar characteristics as the proposed model was substituted instead. Dynamo torchlight was taken apart to be used as a third energy harvesting model for test purposes to determine the efficiency of linear generators as compared to rotary generators.
Power (W)
Time (s)
Time (s)
Time (s)
Figure 8. Dynamo torach light as a substitution for rotary generator model. The maximum output of the rotary model is around 3V at the pneumatic actuating speed of 13.26 cm/s while the minimum voltage presented is approximately 1V.The voltage produced by the device is then passed through the rectifying circuit and measured using NI ELVIS. The output waveform as shown in Figure 9(a) displays that the rotary generating model still produced a significant amount of energy after rectification.
Figure 9 (a) Output Voltage, (b) Energy and power at various speeds.
The measured coil resistance is 17Ω, and using the voltage waveform obtained from the device, the average energy calculated to be 0.18741J while the maximum power generated is 0.25691W. Using the 5 different data sets obtained from the experiment, the relationship between the simulation speed and the energy harvested is again plotted as shown in Fig.9 (b). III DISCUSSION The linear electromagnetic generating model has the performance of the mechanism depends on the speed of the magnet when it is actuated. As shown on Fig. 12b, pulse voltage produced by rotary device is used for harvesting energy. The average energy harvested by the linear generator per second before rectification is 9.8729e-06J while the calculated efficiency based of the energy
loss during a heel strike is 5.74e-04 .The entire mechanism was built using SL 7545 resin instead of aluminum to prevent eddy current and capacitive leakage. Finally, the thickness of the device was reduced to reduce the loss of magnetization and decrease overall weight of the device.. A mechanism with rotary generating characteristics was devised and the human gait cycle was again simulated on the testing platform using the mechanism to harvest energy. IV
CONCLUSION
In conclusion, the human gait cycle was analyzed using EMG, QTM, WinDaq and V3D to provide the basic understanding of human locomotion in order to design a mechanism to harvest energy from heel strike. A total of three mechanisms were built, tested and evaluated based on their performance, cost, feasibility and comfort or the ability to incorporate into daily life. Linear generators are proven to be inefficient in the use of energy harvesting for human locomotion. Therefore, rotary generator was concluded to be more practical as it has a better efficiency while also providing minimal discomfort level to the user. REFERENCES
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