RESNA 26th International Annual Confence

Technology & Disability: Research, Design, Practice & Policy

June 19 to June 23, 2003
Atlanta, Georgia


Andrew J. Rentschler, Rory A. Cooper, Bruce Blasch, Michael L. Boninger
Departments of Bioengineering and Rehabilitation Science and Technology,
University of Pittsburgh
Human Engineering Research Laboratories, VA Pittsburgh Healthcare System 


There are an increasing number of elderly visually impaired individuals in the United States that could benefit from an assistive mobility device that provides navigational assistance. The VA-PAMAID is a robotic walker that can scan the environment and detect obstacles and landmarks. This study determined the safety and performance characteristics of the VA-PAMAID. The results demonstrate that the device presents no hazards to the user and could benefit visually impaired individuals that reside in hospitals or nursing homes. The walker is structurally sound, has a range of 10.9 kilometers, and can effectively detect and avoid obstacles at a speed of 1.2 m/s.


The U.S. Census Bureau study on Americans with disabilities has reported that of 267.7 million non-institutionalized individuals surveyed, 7.6 million had a visual impairment (1). Approximately 1.7 million people are unable to see and another 5.9 million have difficulties seeing words and letters. By the year 2030, there will be 65 million people over the age of 65 (2). There will be 15 million people over the age of 85 by 2050. It has also been shown that visual impairment increases the risk of falls and fractures and thus the likelihood that an older individual may be admitted to a hospital or nursing home (3). The need for effective assistive mobility devices for the elderly and visually impaired will continue to grow. A walker that could provide navigational assistance in addition to support could help reduce the cost of care and increase the independence of many individuals.

The Veterans Administration Personal Adaptive Mobility Aid (VA-PAMAID) is a robotic walker designed to couple the support of a walker with navigational assistance. The walker is equipped with laser and ultrasonic sensors that are mounted on the front and sides of the device. A computer controls the motors that guide the direction of the front wheels. The sensors detect obstacles and landmark features and the walker then gives auditory feedback as well as actively avoiding collisions with obstacles.


The objective of this study was to determine if the VA-PAMAID is a safe and effective mobility aid that can be used to assist elderly individuals with mobility and visual impairments. The performance characteristics of the device were tested to determine if the walker presented any hazards to possible users.


The VA-PAMAID combines the stability of a regular walker with the technology of obstacle avoidance software. Currently, there is not a specific set of standards that establishes safety and performance constraints for such a device. The test plan developed for the VA-PAMAID was created by using information from both the International Standards Organization for walking aids and the ANSI/RESNA wheelchair standards (4,5). The test protocol included sections for static stability, range, maximum effective speed, obstacle climbing ability, climatic conditioning, and strength testing.

The walker was tested for static stability in the uphill, downhill, and sideway directions. A 250N vertical load was applied to the midpoint of the handlebars.

The range of the walker was determined by pushing the device around the VA Hospital until the batteries depleted. The walker was initially charged for eight hours and a digital speedometer was used to track time and distance.

The maximum effective speed of the walker was determined by pushing the device towards a wall in automatic mode at increasing speeds until the walker could no longer avoid a collision. A trailing wheel was attached to the walker to calculate the speed and acceleration for each trial.

The obstacle climbing ability of the walker was determined by pushing the device onto a test platform of adjustable height. The walker was given a 0.5-meter run up as well as being placed directly in front of the platform.

Climatic testing was conducted by placing the walker in an environmental chamber at different temperatures. The temperature was set at 50°C for three hours, -25°C for three hours, 65°C for five hours, and -40°C for five hours.

Static, impact, and fatigue strength testing was performed on the walker according to the ANSI/RESNA wheelchair standards, section 8. An 800 N cyclic load was applied to the midpoint of the handlebars at a rate of 0.15 Hz during the double drum testing.


Table 2- Static stability tipping angles



Roll/Slide/Tip Angle

Tip Angle

Uphill Stability


10º slide




1.0º roll




1.0º roll


Downhill Stability


22º slide




1.0º roll




1.0º roll


Sideways Stability (Facing Right)


13.04º roll




15.3º roll/slide




14.6º roll/slide


Sideways Stability (Facing Left)


9.95º roll




15.0º roll/slide




15.4º roll/slide


The VA-PAMAID traveled a total distance of 10.9 kilometers in automatic mode during the maximum range testing. The elapsed time for this test was six hours and seventeen minutes. The maximum effective speed of the walker was determined to be approximately 1.2m/s. At speeds higher than this, the walker was not able to avoid colliding with the wall. The VA-PAMAID was unable to negotiate an obstacle height of 12mm or higher. The front wheels were not able to overcome this height even with a 0.5m run-up. The walker passed all of the climatic conditioning tests without any failures.

The VA-PAMAID passed all of the static and impact strength tests. The walker also completed 200,000 cycles on the two-drum machine without any failures or problems


The walker was able to travel 10.9 km on fully charged batteries. This distance is an adequate range when compared to the reported distances traveled in other studies. One study of 2678 men between the ages of 71 and 93 found that the average walking distance per day was 1.2 miles (6). A study by the National Institute on Aging found that forty percent of a group of elderly people over the age of 75 could not walk two blocks (7). The average walking distance of an individual using the VA-PAMAID will most likely be even less than these values.

The maximum effective speed of the walker was determined to be 1.2 m/s. A study by the Department of Transportation found that the average walking speed of a group of 3671 seniors was 1.25 m/s (8). Future advances in microprocessing speed and sensor technology should allow for quicker response time by the walker.

The VA-PAMAID has difficulties climbing over obstacles. The device was unable to negotiate a 12 mm high obstacle. The device is designed for use by frail elderly individuals and must therefore be able to easily traverse small obstacles such as rugs, power cords, and door thresholds.

Initial testing of the VA-PAMAID has provided very encouraging results. The device has adequate range, good reaction time, and is structurally and environmentally sound. The next generation walker is already being developed and will incorporate lighter materials and new avoidance software. Clinical trials are also getting under way to compare the VA-PAMAID to another low tech adaptive mobility device and determine if the walker will improve safety, efficiency, and the activity of the users.


  1. US Census Bureau. Americans with Disabilities- Household Economic Studies. 1997.
  2. MacRitchie RF. Reducing the incidence of falls among elderly nursing home residents: an evaluation of an ameliorative pilot program. Southern Connecticut State University. May 2001.
  3. Ivers RQ, Cumming RG, Mitchell P, Attebo K. Visual impairment and falls in older adults: the Blue Mountain Eyes Study. J Am Geriatric Soc. 46:58-64, 1998.
  4. International Standard- Walking aids manipulated by both arms- Requirements and test methods- Part 2: Rollators.
  5. ANSI/RESNA wheelchair standards, Sections 1,2. 1997.
  6. Hakim AA, Curb, JD, Petrovich H, et al. Effects of walking on coronary heart disease in elderly men. The Honolulu Heart Program. Circulation (7) 1999;100:6-13.
  7. Council Close-Up. Today's elderly: physically unfit. April 7, 1995. Number 2.
  8. Knoblauch RL, Pietrucha MT, Nitzburg M. Field studies of pedestrian walking speed and start-up time. Transportation Research Record 1538. Dec. 1996; 27-38.


This project was supported by funding by the VA Research and Development Merit Review C2272R

Andrew Rentschler
Center of Excellence for Wheelchairs & Related Technologies
7180 Highland Drive, 151R-1
Pittsburgh, PA 15206
(412) 365-4850
(412) 365-4858 (fax)

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