Session F4G
The Development and Implementation of a Freshman Engineering Project in Energy Scavenging Yanfei Liu and Carlos Pomalaza-Ráez Indiana University – Purdue University Fort Wayne,
[email protected],
[email protected] Abstract - Energy scavenging from the environment is a contemporary topic that positively benefits society. This paper describes the development and implementation of an energy scavenging project that uses piezoelectric material. In the fall of 2009, this project was implemented in an introduction to engineering course with over one hundred students from four different engineering disciplines: civil, computer, electrical, and mechanical. Survey results and students’ reflection papers showed that the project was appealing to the students and helped them understand several basic concepts as well as principles of the engineering design process. Index Terms – Energy scavenging, freshman engineering, piezoelectric, vibrating system. INTRODUCTION In our school, ENGR/ETCS 101 - Introduction to Engineering, Technology, and Computer Science is a one hour per week course specifically aimed to first year engineering and engineering technology students. The overall purpose of this course is to prepare students for a successful academic performance, to introduce the engineering field, and to make students aware of the engineering problem solving strategy. The current course outcomes are: 1. Understand and apply the concepts of professional and ethical responsibility. 2. Communicate effectively through essays and reports. 3. Understand the engineering profession and appreciate the contributions of engineers and engineering to today's society. In order to achieve these outcomes, students are asked throughout the semester to read material in their textbook [1] and news articles and to write memos and essays. They are also given a series of lectures about engineering and technology fields of study. To gain an understanding of professional ethics, they are asked to apply the engineering code of ethics to a real case. For the past several semesters the case has been the I-35W bridge collapse in Minnesota that took place in 2007 [2].
Before the fall of 2009, a reverse engineering project was used as a group project to give students experience in engineering problem solving strategies. The reverse engineering project requires students, working in groups, to find and research a specific device, disassemble it, and understand how the device works. Students are also asked to conduct quantitative measurements related to the device. The reverse engineering project always faced the challenge of finding a device with the right level of complexity. Students often had difficulties conducting enough quantitative experiments to gain experience in engineering problem solving strategies. When ETCS/ENGR 101 was first launched (in 1999) students were asked to design, build, and test an autonomous robot using the Lego Challenger set (similar to the Lego Mindstorms set) that had recently become available. This project proved to be very successful and played an important role in improving the retention of engineering and technology students [3]. The project was discontinued in 2003 because the instructors involved with the course moved into different academic roles and there was no one else in the faculty with the expertise and desire to continue having such project in this course. It has been ten years since this course was introduced, so a new project is needed to address contemporary issues. The topic of scavenging energy from the environment is an area that we have been exploring within our own research interests. Having a project in this area not only falls within our academic interests but it also has a great deal of societal impact. This type of project fits very well the requirements of the IEEE Real-World Engineering Projects (RWEP) program that funds high-quality, tested, hands-on teambased society-focused projects for first-year students. These projects are designed to increase the recruitment, persistence to degree, and satisfaction of all students, and particularly women, in baccalaureate EE, CE, CS, BE and EET degree programs. We then decided, in April 2009, to introduce a freshman level design project in energy scavenging through vibrations using piezoelectric material. At the same time this project was proposed to the IEEE RWEP program [4]. The project was developed during the summer of 2009 and first implemented in the fall of 2009 with over one hundred students in five sections of ENGR/ETCS 101. After three review stages, this project has been accepted by the IEEE RWEP program, and it is in its final revision phase.
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-1
Session F4G
(a) The prototype station
(b) The cam location FIGURE 1 AN EXAMPLE OF A TESTING STATION.
UNIQUE FEATURES OF THIS PROJECT There are two major features of this project that makes it unique when compared to other freshman engineering design projects. One, to the best of our knowledge this project is the first design project in energy scavenging that includes a vibrating system and piezo-electric materials given at a freshmen level, or at an undergraduate level. Efficient design of an energy scavenging system using piezo-electric materials are topics for Master’s thesis or even Ph.D. dissertations. Two, unlike conventional freshmen engineering design projects that target a particular engineering field, this project combines elements from electrical engineering (energy harvesting circuitry), computer engineering (data acquisition), mechanical engineering and civil engineering (vibrations). This project helps students in two ways. For students who haven’t decided on a specific engineering field, the project gives them a good exposure of different engineering fields via hands-on activities. Also, this project helps student gain multi-disciplinary experience during their freshmen year. PROJECT DEVELOPMENT We started the development of the project in the summer of 2009 by first selecting the DC motor, the piezo electric device and the components used to generate vibrations. The Lego Challenger sets that were used in the robotics handson project, mentioned in the introduction section, had been left in a storage room for several years. Lego pieces, including bricks, beams, axles, gears, offer great flexibility and yet enough complexity for students to design and build a large variety of systems. Because Lego pieces can be readily obtained this project can be easily adopted by any other school worldwide. For our institution using Lego pieces as the main components for the vibrating system minimized the implementation costs. A simple vibrating station composed of Lego pieces and a DC motor was first built as a prototype to test the performance of three different
piezo buzzers bought from RadioShack. Figure 1 shows pictures of the prototype. When the project was implemented in the fall of 2009, students generated many different and creative designs. Examples of students’ work will be described in later sections. To harvest the energy produced by the piezo buzzer, a circuit that includes a rectifier and an energy-storage subsystem is needed. The system adopted for this project is a circuit slightly modified from the one in [5]. Figure 2 shows the circuitry. Two NiMH rechargeable batteries (button cells) rated at 40 mAh and 80 mAh were tested. It was decided to use the one with the lower rating for effective results.
FIGURE 2 ENERGY SCAVENGING CIRCUITRY.
PROJECT DESCRIPTION In this project, students conduct energy scavenging experiments with a piezoelectric device. The design process can be broken into the following steps: 1. Design and construction of a vibrating system. 2. Experimental measurements, data acquisition and analysis. 3. Use of an energy harvesting circuitry to charge a battery. The design component of this project is the construction of a vibrating system that will be used to experiment on energy harvesting using a piezo buzzer. Each team is asked to design two test stations that generate vibrations of
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-2
Session F4G different amplitudes and frequencies. In one test station a gear train needs to be designed for the vibrating system to match as closely as possible the given resonant frequency of a piezo buzzer. Figure 3 shows a sample of the components provided. Students had access to a larger amount of Lego pieces than the ones shown in Figure 3.
values of the speed of the motor and the resonant frequencies of the piezo buzzers.
FIGURE 4 A SCREENSHOT OF THE VIRTINS MULTI INSTRUMENT PRO 3.1.
FIGURE 3 A SAMPLE OF COMPONENTS PROVIDED TO STUDENTS.
To test and evaluate the effectiveness of their design, students are asked to measure and observe the electrical signals generated by the piezo buzzer due to the vibrations. In order to minimize the costs of the project it was important to be able to do this task without the use of a physical oscilloscope. We used software oscilloscopes which are available from several suppliers. The price of these oscilloscopes is relatively low (less than $30 per copy). Since they use the computer’s audio card (the microphone input) a special cable is needed which can be bought (around $30 per cable) or built at a much less cost. We decided to use the latter option which has the drawback of the labor time dedicated to make them and the need to use a voltage divider to match the output of the piezobuzzer to the input of the PC audio card. For our project we used a decade resistor box to implement the voltage divider and the Virtins Multi Instrument Pro 3.1 as the software scope. Figure 4 shows a screenshot with callouts describing the software functions. After the experimental measurements, students connect the piezo buzzer from their vibrating system to the energy harvesting circuit (Figure 2) built on a breadboard (Figure 5) to charge a 40mA cell button battery. DESIGN TRADE-OFFS AND CONSTRAINTS Each team is asked to design two types of testing stations to generate vibrations for the piezo buzzer. One of the designs does not gear down or up the motor. The other design should include a gearbox with different gear ratios so that it decreases or increases the speed of the motor to match the resonant frequency of the piezo buzzer. The gearbox must be designed based on the ratios between the quantized
FIGURE 5 ENERGY HARVESTING CIRCUIT ON THE BREADBOARD.
The gearbox is constructed using Lego gears. Having a gearbox provides a better chance for the piezo buzzer to generate the largest response. The comparison of the output voltage responses of the piezo buzzer using the two different testing stations can illustrate the tradeoff between design complexity and energy generated. The more complex the design is, the longer the time and higher the costs it takes to implement it, but the more energy it should generate. The designed system has to meet the following constraints: • Vibration frequency as close as possible to the resonant frequency of the piezo buzzer • Size limited to 12’’ x 8’’ x 6’’ (L x H x W) • The vibrating system should be able to continuously work for at least half an hour • A minimum of 2 volts peak to peak output signal from the piezo-buzzer • The use of glue, tape, or any bondage substance that permanently connects the Lego pieces are not allowed (the same rule applies to the piezo-buzzer)
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-3
Session F4G
FIGURE 5 STUDENTS WORKING ON THE PROJECT.
STUDENTS’ ACTIVITIES This project is a group activity. Each section was divided into groups of 3 or 4 students. Figure 5 shows students working on the project. We learned from this first implementation of the project that 4 students are too many in one single group. So in the spring 2010 semester we divided each section into groups of 2 or 3 students. The comparison between the projects’ performance corresponding to each semester will help us determine the appropriate number of students per group. The project takes fifteen hours to accomplish. Two and a half hours are dedicated to the lectures that provide background information, instructions on the experimental measurements, and a summary. In our school, six weeks were allocated to the project. In each week there are 50 minutes of class time dedicated to the project. Students still need to find time outside the class to build their final design and conduct experimental tests. The timeline for students’ activities expressed in hours is shown in Table I. After the first lecture students are asked to brainstorm and write initial design proposals prior to the next lecture. To help them with this process several small plastic boxes, each with a sample of the Lego pieces as well as the motor and the piezo buzzer is made available to them on a check-out basis.
TABLE I TIMELINE OF STUDENTS ACTIVITIES Students Activities
Timeline
Initial Vibrating System Design
2.5 hours
Construction, Experimental Measurements, Tests, and Evaluation
8 hours
Report Writing
2 hours
STUDENTS’ WORK Figure 6 shows the pictures of two vibrating systems designed and built by one of the teams who took ENGR/ETCS 101 in the fall of 2009. Figure 7 shows the experimental measurements for the two designs shown in Figure 6. The measurements include the waveform and the frequency spectrum of the output voltage from the piezo buzzer while vibrating. Figure 8 shows the experimental results when the battery was being charged for 30 minutes using both designs separately. Within the 30 minutes the voltage across the battery was measured every 5 minutes. The plot of the voltage vs. time can be seen in Figure 8. These measurements show that the design with gear trains (design 2) had a better charging performance.
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-4
Session F4G
(a) Design 1: without a gear train
(b) Design 2: with a gear train
FIGURE 6 PICTURES OF TWO VIBRATING SYSTEMS BUILT BY STUDENTS.
(a) Design 1
(b) Design 2 FIGURE 7 EXPERIMENTAL MEASUREMENTS, OUTPUT VOLTAGE AND FREQUENCY SPECTRUM.
(a) Design 1
(b) Design 2 FIGURE 8 BATTERY CHARGING RESULTS (VOLTAGE VS. TIME).
IMPLEMENTATION CHALLENGES One of the IEEE RWEP program’s main requirements for their projects was that the overall cost be kept to a minimum. The intention is that successful projects should be able to be implemented even in regions in the world
where laboratory resources are scarce or too expensive for the host institution. Therefore we used readily available hardware and software components. Case in point, software oscilloscopes were used instead of regular physical oscilloscopes. Other components chosen are simple small
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-5
Session F4G buzzer is and learned about the piezo electric effect. There was a lot of knowledge in this project. I also learned about what kind of work I have to put in for college.” “I really enjoyed this project. It really expanded my knowledge of the electrical and mechanical aspects of engineering.” A common negative comment from students was that the time for a one credit hour course is not enough for this project. “One thing that I would recommend to improve the execution of this project would be to give more time to be able to do it. With more time, I think that the results of the project would be more accurate since we would be able to run more and more tests.”
DC motors, Lego pieces, resistor based voltage dividers, and a small breadboard to implement the rectifying circuit. It was necessary to continuously monitor the work of the students as they progressed in their project since minor complications took place on a regular basis. For example, the button shaped cell battery came without leads. To make connections in the breadboard, two wires were soldered to each battery ends. This soldering can become lose with time and thus it is suggested that it be executed in the best possible way. After the soldering a small strip of tape wrapped around the battery ends was used to reinforce the connection. However soldering on a button cell battery can be dangerous. Therefore in spring 2010 we switched to using small plastic clothes clips to keep the wire leads tightly attached to the battery ends.
DISCUSSIONS AND CONCLUSION This paper describes the development and implementation of a freshman engineering group hands-on project in energy scavenging. The project was first implemented in the fall of 2009. The pre- and post-survey results and students’ comments from the reflection paper showed that this project is a helpful and a very enjoyable learning experience.
STUDENTS’ FEEDBACK In the fall of 2009 a survey was given to the students, before they started the project, to assess their understanding of the following concepts: diode, AC vs. DC, gear ratio, simple gear train, compound gear train, frequency, spectrum, asymmetric cam, signal rectifying, and harmonic vibration. Students were asked to rate their understanding of these concepts using a score range of 1-5. After the project was finished, a post survey on the same concepts was conducted. Figure 9 shows a chart comparing the pre- and post-survey results. These results show a significant improvement in the understanding of the concepts. More detailed results showing the responses of students depending on their major were presented in [6]. Since these students are in an early stage of their studies, there are no significant differences of their responses from major to major. At the end of the project, students wrote a reflection paper about their experiences with the project. Some comments from the students are: “Personally this project definitely helped me learn a little bit more of just what an engineer does everyday. It helped me to see that it involves lots of time, perseverance, and ingenuity to attain a specific goal, but once you reach the said goal, it can be a very beneficial thing to you and those around you.” “The benefits that I received were in knowledge. I learned a lot about electronics that I never knew before and about how to run and execute test electronics. I also learned what a piezo
ACKNOWLEDGMENTS The authors would like to thank the Department of Engineering at IPFW for the financial support to the implementation of the project. REFERENCES [1] [2]
[3]
[4] [5] [6]
Engineering, a compilation published by McGraw-Hill, Inc., 2007 L. Blake, P. Mcenroe, P. Doyle and T. Kennedy, “MnDOT feared cracking in bridge but opted against making repairs,” in Star Tribune, August 3, 2007, http://www.startribune.com/local/11593616.html, Accessed March 2010. C.A. Pomalaza-Ráez and B.H. Groff, “Retention 101: Where Robots Go…Students Follow,” ASEE Journal of Engineering Education, January 2003. IEEE Real World Engineering Projects Program, http://www.realworldengineering.org/, Accessed March 2010. C. Cossio, “Harvest energy using a piezoelectric buzzer,” EDN, pg. 94-96, March 20, 2008. Y. Liu and C. Pomalaza-Ráez, “Concept Learning Embedded in a Freshman Engineering Project in Energy Scavenging,” in Proceedings of 2010 International Conference on Education and Educational Technology (EET), Wuhan, China, May 10-11, 2010
Pre‐ and Post‐Survey Results Pre
Post
4 3 2 1 0 Diode
AC vs DC
Gear Ratio
Simple Gear Train
Compound Asymmetric Gear Train Cam
Frequency
Spectrum
Signal Rectifying
Harmonic Vibration
FIGURE 9 PRE- AND POST- SURVEY RESULTS.
978-1-4244-6262-9/10/$26.00 ©2010 IEEE October 27 - 30, 2010, Washington, DC 40th ASEE/IEEE Frontiers in Education Conference F4G-6
