Grasping Tool for Disabled Man
Undergraduate Engineers Use Battery, Motors and Software
to Provide 'Helping Hand'
Using two motors, speech-recognition software and an exo-skeleton inspired by science fiction, three Johns Hopkins University undergraduates have designed and built a muscle enhancement device that will help a disabled man grasp and lift a cup, a book and other household items. By uttering commands such as "open" and "raise," the man will receive mechanical help in moving his fingers and bending his elbow. The motorized plastic shell will fit over the right arm of the man, who has an extremely rare degenerative muscle disorder called inclusion body myositis
This device, which could be adapted for other people with disabilities, was developed during two semesters by students in the Department of Mechanical Engineering's Senior Design Project course. The project originated last summer when the man with the muscle disease sought help from Volunteers for Medical Engineering, a nonprofit Baltimore group that uses technology to assist people with disabilities. The client, who asked that his name not be disclosed, explained that his nerves were intact, meaning that he could control the placement of his fingers around an object. But progressive muscle deterioration left him unable to grasp and lift even small objects.
To help him, the VME sponsored a project in the Johns Hopkins course. The task of designing and building the device went to a team consisting of three senior students: Jonathan Hofeller, 21, a mechanical engineering major from Needham, Mass.; Christina Peace, 21, a biomedical engineering major from Baltimore; and Nathaniel Young, 22, a biomedical engineering major from Dayton, Ohio. The students researched prosthetic limbs and, taking a cue from props featured in the film "Aliens," they designed a plastic exo-skeleton that could slide over the client's right hand and arm. To help move his fingers and elbow, the students tested and rejected systems using electromagnets and air pressure systems. They finally settled on two small but powerful stepper motors. These could move the fingers and elbow in small, slow increments, allowing the client to clasp a cup firmly without crushing it. In addition, these motors did not require continuous electrical current to stay in position, which preserves battery power. The students linked the motors to a series of cables and springs to enable the device to move the man's arm into position and help his fingers grasp and release.
The students opted for voice recognition software as an easy way for the disabled man to control the grasping device. After the software is trained to the client's voice, the man will first say "arm" or "hand" to take command of one of the two motors. The elbow motor will then respond to "raise," "down" or "stop." The hand motor will respond to "open," close" and "stop." The device is hard-wired to a control box that contains a miniature computer and two programs that turn the voice commands into signals that tell the motors how to operate the bending and grasping motions. The unit is powered by a rechargeable 12-volt lead-acid battery commonly used for remote-control model boats and airplanes. The control box fits inside a small pack the man can carry on his waist, making the grasping the device fully portable.
"The students did a wonderful job," said Jan Hoffberger, executive director of Volunteers for Medical Engineering. "They came up with a very creative design for the device. They purposely set it up to move very slowly, so that at any time in the grasping and lifting process, our client can tell it to stop. We believe he will find it very helpful."
The students had to work within a budget of $10,000; they ended up spending about $8,000 on the device. Designing and building it helped the undergraduates to understand some of the challenges that working engineers face. "In a textbook, there is always one right answer," said Young. "In this project there were many different ways we could go, but once we were committed we had to go in that direction." His teammate, Hofeller, said, "The project involved a lot of trial and error, but it was fun to apply what we've been learning." The third team member, Peace, added, "When you're working out a problem in an engineering book, the conditions are ideal. In this project, the conditions were not perfect, but we still got the job done."
The grip enhancing device was one of 11 Johns Hopkins projects completed this year by undergraduates in the Senior Design Project 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 two or three 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.
Color images of the device and the students available; contact Phil Sneiderman
Follow this link to more pictures of the grasping device.
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