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Students Design Auto Harness to Protect Elderly,
Others With Brittle Bone Disorders
May 24, 2004 - When a car crash occurs, people with
osteoporosis and other brittle bone disorders often suffer more serious
injuries. To better protect these fragile motorists, three Johns
Hopkins undergraduate engineering students have devised a harness and
vest system that significantly reduced impact forces when tested on a
high-tech crash dummy.
The students were responding to a challenge from
the Center for Injury Research and Policy in the Bloomberg School of
Public Health at Johns Hopkins. We estimate that as many as 13 million
people with osteoporosis, osteogenesis impefecta (brittle bone disorder)
and hemophilia need some additional protection from forces applied to
the torso during a car crash, said Gary S. Sorock, an associate
professor at the center. The assignment was to design and test a
restraint system that would reduce these forces, protecting the ribs and
the sternum in particular.
During their two-semester Engineering Design
Project course in the Department of Mechanical Engineering, the team of
three seniors addressed this problem. The team designed a vest filled
with three layers of foam padding, each with a different density, to
absorb some of the energy that causes a motorists chest to compress
during a crash. In people with weakened bones, this compression can lead
to broken ribs and other serious internal injuries. The students also
replaced a conventional three-point shoulder belt with a four-point race
car harness, which distributes the crash forces across a wider area of
the body and keeps the body in a tighter fit against the seat.
In May, the students brought their system to the
Impact Biomechanics Test Facility at The Johns Hopkins University
Applied Physics Laboratory. The staff assisted the students in
conducting tests on a dummy that simulated a 108-pound woman, belted
onto a sled moving at an average speed of 18.5 mph. The dummy was
equipped with sensors to gauge the effect on various parts of the body
during the equivalent of a 20-mph head-on crash or a 35- to 40-mph crash
involving a moving car striking a parked vehicle. A high-speed camera
mounted on the crash sled also captured closeup images of the dummy as
it was jarred by the impact.
The students tested the dummy with a conventional
shoulder belt alone, with a shoulder belt and their prototype
foam-filled vest, with the four-point harness alone, and finally with
both the harness and vest. When the dummy was outfitted with the vest
under the conventional restraint, chest compression was reduced by
approximately 8 percent (from 26.9 to 24.9 millimeters). Testing with
the harness provided a different loading mechanism to the dummy torso
and created much less sternum deflection (3.5 millimeters). Despite the
reduced loading, the addition of the vest further decreased the sternal
compression by 17 percent to 2.9 millimeters. The students also compared
crash impact forces, measured from the seatbelt. This dropped from 644
pounds of force with the standard shoulder belt alone to about 436
pounds with the harness.
The student inventors, all seniors, were Richard
Chen, a 21-year-old biomedical engineering major from Lexington, Ky.;
Patrick Danaher, a 23-year-old mechanical engineering major from
Bedford, Mass.; and Ryan Lavender, a 21-year-old mechanical engineering
major from Atco, N.J. They were required to work within a sponsored
budget of $8,000 but wound up spending only about $5,500 to produce the
crash protection system.
These students have done a very nice job of
tackling a very difficult problem, said Andrew Merkle, an associate
researcher at the Applied Physics Laboratorys Biomechanics and Injury
Prevention Office. Merkle supervised the students crash dummy tests.
We were happy to see the reduction in blunt force
upon the dummy using this system, Chen said. The vest might also have
some applications in helping to prevent injuries in sports like football
or snowboarding.
Lavender agreed. I think the vest has the
potential to help a much wider audience than I originally thought, he
said. I can see it protecting older people and children from injuries.
Danaher enjoyed putting the knowledge hed acquired
in other engineering classes to use in the type of team project he may
face soon in the working world. The senior design course was
incredible, he said. It gives you the kind of hands-on challenge that
many other college students dont get the chance to experience.
The crash protection system was one of nine Johns
Hopkins projects completed this year by undergraduates in the
engineering design course. The class is taught by Andrew F. Conn, a
Johns Hopkins graduate with more than 30 years of experience in public
and private research and development. Each team of three or four
students, working within budgets of up to $10,000, had to design a
device, purchase or fabricate the parts, and assemble the final product.
Corporations, government agencies and nonprofit groups provided the
assignments and funding. The course is traditionally a well-received,
hands-on engineering experience for Johns Hopkins undergraduates.
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