 | |
| Vol. 18, No. 35 | June 24, 1999 |
| |
| Vol. 18, No. 35 | June 24, 1999 |
UD engineering students (from left) Jason Firko, Matt Behr and Allan Cohen
worked with Dave Bartoski to create a watermelon ripeness sensor.
The course, System Design and Synthesis-I and II (MEEG 447-448), is an example of project-based learning, said class coordinator Dick Wilkins, mechanical engineering. "Learning occurs through solving problems, rather than through classroom lectures," he said. "In this case, students work in true-to-life projects with real customers, real budgets and real expectations."
Michael Keefe, mechanical engineering, and James Glancey of bioresources engineering and mechanical engineering, supervised 14 teams of students, including four assigned to solve agricultural problems.
One team invention, a ripeness sensor for watermelons, tied for third place in the American Society of Mechanical Engineers competition held this spring at UD. (See the article on page 5 for more information on other award-winning inventions.)
Delaware farmers grow more than $6 million worth of watermelons that they sell, each summer, to fresh produce markets from Maine to Florida. But, sensing when a melon is ripe is not at all easy, according to Ed Kee, a UD extension specialist for vegetable crops. Harvesting green melons can mean a serious economic loss for farmers, he said.
"It's not at all unusual for a 40,000-pound truckload of watermelons to be rejected in the marketplace," Kee explained. "If even 10 melons are green, the whole load could be rejected. Worse, if melons were delivered to Boston, for example, and rejected there, then the farmer pays the freight both ways, losing about $5,000 to $6,000 for the truckload."
To solve this problem, Kee wanted a machine to accurately predict when a watermelon is ripe-with a sugar content of 8 to 12 percent. The machine should be fast and easy to use. It should be inexpensive and portable to take into the field. UD design students Dave Bartoski, Matt Behr, Allan Cohen and Jason Firko worked with Kee to develop just such a device.
Collecting clues about the contents of a watermelon was the first hurdle, Behr said.
"First, we considered nuclear magnetic resonance scans, but they average $80,000, so that was out," he said. "Then, we considered ultrasound, but that didn't work because sound waves can't get through a melon. Finally, we settled on the old fashioned way-thumping the melon and listening to sound."
The machine's central feature is a platform where the watermelon rests. Sandwiched between the platform and the melon, a piece of foam rubber holds it steady. A mallet attached to a metal arm protrudes from the machine on the right, while a microphone sits close to the melon on the left.
How does the machine work? When Behr swings the metal arm, the mallet strikes the melon. The microphone picks up the sound and transfers it via electric signal to a laptop computer. The voltage signal is then converted into digital information, which is analyzed.
Because the hollow thunk of a ripe melon echoes, it produces an acoustical signal that shows up as a peak on the computer screen, which dies down gradually.
On melons tested thus far, the frequency of the signal, when normalized using volume, has shown a promising correlation to the actual sugar content of the melon.
The size of the watermelon influences the frequency of the signal and, therefore, is taken into account during analysis, Behr notes.
Melon characteristic frequencies have ranged from 100 to 250 hertz, corresponding to the desired sugar content of 8 to 12 percent. These findings will be put to the test this summer, as researchers investigate many more melons.
The work remains preliminary, Behr said, but early results are promising: "The device is fast, cycling in 12 seconds, and it's easy to use," he said. "The electronics are sealed to keep out the dirt. It's durable and easy to maintain."
It also works continuously for more than four hours, with one battery. It costs less than $1,100, and weighs only 18.2 pounds. It even comes with Velcro straps so the computer and the sensor can be carried conveniently into the field.
"We knew the project would be complicated because we'd be working with melons that are all weird sizes and geometries and varieties, but it's a lot more interesting this way," Behr said. "We learned a lot, too."
Kee said he has been "really impressed with the students and the work they have done. Growers are excited that, finally, someone is coming up with the concept of a ripeness sensor. We're looking at the first generation of a machine that will be proven this summer and, quite possibly, will go commercial down the road."
Ultimately, Kee said, "We envision a hand-held microprocessor to replace the laptop computer as the final form of this machine." Since the National Watermelon Association reports that 1.5 trillion pounds of watermelons currently are sold in 90 countries on five continents, "the marketing potential for this machine is excellent," he added.
Moreover, he said, "This project is a great example of melding the teaching, research, and extension components of the University to address real world situations. It's exciting and fun when these parts come together."
For information on the senior design project, contact Wilkins at (302) 831-2006 or <wilkins@ udel.edu>.
-Pat McAdams
Photo by Duane Perry
