Electronic Design

Smart Walker Detects Obstacles

A research team at the University of Virginia's Medical Automation Research Center in Charlottesville has developed a prototype "smart" walker. This mobility aid should improve the quality of life and lengthen the duration of independent living among the world's elderly.

The intelligent walker improves safety through features such as obstacle avoidance and drop-off detection. This lets users navigate traditionally difficult situations, such as tight spaces and doorways. It also reduces the risk of catching a wheel on an object. And, the smart walker helps users follow a specific route through an environment.

This prototype is considered a passive robot. Since it can only control the orientation of its front wheel and cannot move forward on its own, it requires a human to move it. Its control system is an intelligent agent that provides support and navigation assistance. This agent studies the movement of the walker frame and the sensor systems to derive a model of the user. It then attempts to decipher where the user may be going.

When the control agent is actively helping the user steer, the control system and the user input control signals to the walker frame. The researchers say that each agent learns about the other by observing the walker's resulting motion. The agent's ability to implicitly formulate the user's goals allows the user to employ this device in a seamless manner. When the desires of the user and the agent differ, the user's actions take priority.

However, the walker control agent assumes complete control when a collision or drop-off is imminent and the brakes must be applied. The researchers say the walker can assume a more or less active role in guiding its user depending upon the user's abilities at any given time. The ability to alter this degree of autonomy is an ongoing area of research.

The prototype walker is based on a conventional three-wheeled frame from InvaCare Corp. of Elyria, Ohio (see the figure). This frame has been augmented with sensors and actuators to control the front wheel and the brakes. Mounted on the front of the walker, a laser scanner provides a depth map for a 180° field of view in front of the walker. IR sensors are being installed to monitor for collisions with the back wheels. Encoders have been mounted on all three wheels. These devices let the smart walker determine the path taken by the user as well as the likely direction the user will take next.

The drive system is a belt-driven stepper motor system capable of turning the front wheel to a given heading. Since the drive system can only control the front wheel's orientation, the user must provide the motive force. Currently, the prototype features hand brakes. A motorized brake system has been designed to activate the existing brakes on the rear wheels. Thus, the walker can be stopped conventionally by the user or halted by the control system in the event of a dangerous situation.

The prototype also is being outfitted with handle sensors to detect the force planes on each handle. These sensors provide both an indication of the movement taken by the user and detection of the user's desire prior to the movement of the walker.

For more information, point your browser to http://marc.med.virginia.edu.

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