More Info on the GuideCane

From: Lloyd G. Rasmussen (lras@loc.gov)
Date: Thu Oct 09 1997 - 12:15:50 PDT


The following is copied from IEEE Spectrum, October 1997. It gives us
a better idea of the capabilities of the GuideCane from the
University of Michigan.

I didn't find very much useful information on the inventor's web page:
http://www-personal.engin.umich.edu/~johannb/

but maybe I didn't look in the right place.

 

                                  [INLINE
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Seeing-eye cane steers the blin

   A new type of electronic navigational aid for the blind may soon joi
   white canes and seeing-eye dogs. Developed by scientists at th
   University of Michigan in Ann Arbor, the GuideCane is an array o
   ultrasonic obstacle-sensors attached to a wheeled handle, or cane
  
   Operation is simple. The user selects a direction of travel--say
   ahead--by using a joy stick on the cane. He or she then pushes th
   GuideCane forward with one hand, much as if it were a golf cart. T
   turn right or left, the person presses the joy stick to the right o
   left, whereupon a servo turns the wheels in the appropriate direction
  
   When the sensors detect an obstacle, an on-board 25-MHz 486 compute
   determines the best path around it and directs the servo to turn th
   guide wheels. Through the cane, the user feels the change in directio
   and follows. After the obstacle is passed, the cane brings the use
   back to the desired direction of travel
  
   The GuideCane weighs only 4 kg, because it does not have to supply it
   own driving power. As a result, it may be picked up and carrie
   upstairs or down, if necessary, explained the unit's inventor, Johan
   Borenstein, head of the Mobile Robotics Laboratory in the university'
   department of mechanical engineering and applied mechanics
  
   The prototype GuideCane, built by graduate student Iwan Ulrich, has 1
   sensors and can sense any obstacle within a 120-degree angle in fron
   of the user [see figure]. The sensors, made by Polaroid Corp.
   Cambridge, Mass., are the same as those used to focus camera
   automatically, and they operate in much the same way. They each emit
   pulse of ultrasound and wait for the echo. The interval between th
   two events determines the distance to the obstacle, while th
   orientation of the particular sensor that detects the reflected puls
   determines the angle. Whenever a sensor detects an obstacle, th
   information is passed along to the computer for it to enter the new
   on a two-dimensional occupancy grid of 10-by-10-cm squares. Thus a
   all times the computer possesses a map of the obstacles in the are
   around the cane
  
   "But what good is a map of obstacles," asked Borenstein, "if th
   GuideCane doesn't know where it is on the map?" So the uni
   incorporates odometry to keep track of its location. Encoders on th
   guide wheels measure their rotation to a fraction of a revolution
   This is translated into the distance traveled from a point of origin
   When the GuideCane swivels, one wheel moves farther than the other
   and the information is related back to a direction. To eliminate th
   errors that accumulate in this type of measurement, Borenstein plan
   to add a compass so that all measurements can be tied to magneti
   north
  
   The inventor has added a couple of his own patented algorithms to th
   GuideCane's arsenal of obstacle avoidance techniques. One of the
   calculates the best path around obstacles, based on information fro
   the occupancy grid. The other addresses the uncertainty that
   reflection received by a sensor echoes its own pulse. In a typica
   environment, the pulses undergo multiple reflections. Other thing
   being equal, the uncertainty could force a wait to fire a pulse unti
   the echoes from a previously fired sensor have died away. Bu
   Borenstein's method attaches signatures to the pulses so that eac
   sensor can determine whether an echo came from its own or another'
   pulse. Because the sensors can now fire more often, much faster trave
   speeds are open to the user
  
   At the moment Borenstein is grappling with more immediate issues, suc
   as the GuideCane's ability to detect different surfaces. The use
   should be able to recognize that he is veering off onto someone'
   lawn, for example. To solve this problem, Borenstein plans to fring
   the sides of the GuideCane with whiskers, which will sense the edge o
   the grass. Normally, the tips of the whiskers will be a couple o
   centimeters above the cement; but if the Cane starts to veer off th
   sidewalk, the user will feel and hear the whiskers brushing along th
   lawn
  
   A second problem is less tractable and is due to specular reflection
   When ultrasound pulses from a sensor bounce off smooth surfaces lik
   windows or mirrors, they do not reflect back to the sensor unless th
   surface is directly ahead. So if the person is approaching, say,
   glass wall at an oblique angle, the wall may be invisible to th
   GuideCane, and a collision may result. This is not the worst thin
   that can happen, Borenstein believes, since it is the GuideCane tha
   is colliding with the surface and not the blind user. Nevertheless, i
   is inelegant. "There is no good solution for this," Borenstein tol
   IEEE Spectrum. "The most practical solution is a good bumper aroun
   the GuideCane.
  
   "A preliminary version of the prototype has been tested by visuall
   impaired individuals and the reaction was extremely positive," sai
   Borenstein. "But more development will be required before the devic
   is ready for widespread commercial use.
     ________________________________________________________________
  
                                                    Linda Geppert, Edito
     ________________________________________________________________
  
                       contents feedback search hom
  
               IEEE Spectrum October 1997 Volume 34 Number 1
                                     
      (c) Copyright 1997, The Institute of Electrical and Electronic
                              Engineers, Inc



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