ENGINEERING INSIGHT
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The ACT3D system creates a virtual world designed to help stroke victims regain a measure of control over their limbs.
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Taking products that are on the market and using them to create something new and better is a foundation of design technology. That is what happened when Jules Dewald, PhD, associate professor of physical therapy and human movement sciences, physical medicine, and rehabilitation and biomedical engineering at Northwestern University (Chicago, IL, USA), and Wim Lam, owner and general manager of Lam Design Management (Orchard Park, NY, USA), joined forces to develop a new type of robotic system for the rehabilitation of stroke victims.
“Lam has the engineering, and I have the scientific background. It was an ideal match,” says Dewald. “Together, we developed a new system and a new business, D.L. Rehab Technology.”
Creating the system was a blended process. Dewald had been doing in-depth research in stroke rehabilitation for years. He had conducted extensive research using custom load-cell sensors developed by JR3 Inc. (Woodland, CA, USA) to record isometric elbow/shoulder torques of the affected upper limbs of stroke victims. Dewald wanted to take it one step further and use the same load cells to monitor subjects when they are reaching out and lifting the weight of their affected arms. Most people who have suffered a stroke find this action very difficult to do unless the arm is fully supported. Typically, an air bearing device that slides over a large table is used.
Lam’s company represented a robot called the HapticMASTER from Netherlands-based Moog FCS B.V. (Nieuw Vennep). While Lam was demonstrating the basic system to Dewald, the two started throwing ideas around. Lam suggested that perhaps the robot could replace a real table with a virtual one for the benefit of stroke victims.
“We wanted to create a virtual world for stroke victims, where the weight of their arm could be fully eliminated and then gradually reintroduced,” says Dewald. System development began in the summer of 2003. Using the best parts of two existing pieces of rehabilitation equipment with a unique new interface developed around the JR3 load cell, the first ACT3D (Arm Coordinated Training Device in Three Dimensions) began to take form.
“We needed to measure not only the forces in the three linear axes, but also the torques. It was necessary to create an interface with the load cell and to design an end effector [the tooling connected to the end of a robotic arm] to accommodate these requirements,” says Lam.
Lam and Moog FCS engineers collaborated on adapting elements of the HapticMASTER and incorporating the JR3 load cell. Relying on data culled from experiments, Dewald and Lam specified a 4.5 ¥ 1.5-in., 100-lb load cell for integration into the end effector.
In addition to the load cell, a chair created by Biodex Medical Devices (Shirley, NY, USA) is a key part of the system. “It incorporates an adjustable seat that moves on a track to accommodate individuals of different sizes. This allows them to be placed in the correct position with respect to the robot. The combination of the Biodex seating arrangement and our modified HapticMASTER robot created the new ACT3D system,” says Lam.
How It Works
The computer creates a virtual world with objects and responds to patients’ movements, so their arms are never forced into a particular position. The robot processes 3-D information, including the position in space where the subject interacts with the end effector, so it generates a sensation of contact with physical objects. The video interface allows subjects to see their arm and the virtual objects in space. Feedback provides a realistic feel to the objects in the virtual environment.
The built-in interface, which supports the hand and forearm, is connected to a gimble, which is attached to the load cell. Via the gimble and a rigid splint support, the tip of the robot is connected to the forearm of the individual patient.
“What is unique is that we can set up the environment to get the maximum benefit from the training,” says Dewald. “Over time, we can make the arm heavier, to the point where the patients can deal with the real weight of the arm as they explore the work space. It’s like two systems in one, first providing a virtual world that allows stroke subjects to move while also continually monitoring their advances in all therapies simultaneously.”
The next iteration of the ACT3D is already in progress. The team of Dewald and Lam is now looking into ways to modify the system to help patients regain hand/finger dexterity. The modification of the first system will begin in earnest in mid-2006, and the goal is to have the device ready for widespread clinical use within 2 years.
