Design Innovation

Vision Aid for Power Wheelchair Users

[+] Author and Article Information
Kyle C. Smith, Carlos A. C. Kemeny, Raymond Cipra

School of Mechanical Engineering, College of Engineering, Purdue University, West Lafayette, IN 47907

Bradley S. Duerstock1

Center for Paralysis Research, School of Veterinary Medicine, Purdue University, 408 South University Sreet, West Lafayette, IN 47907bsd@purdue.edu


Corresponding author.

J. Med. Devices 2(4), 045001 (Nov 19, 2008) (7 pages) doi:10.1115/1.3006347 History: Received March 04, 2008; Revised August 20, 2008; Published November 19, 2008

The sitting posture of power wheelchair (WC) users greatly limits their overall visibility. Without the ability to stand or lean forward, WC users are prevented from peering over most obstacles and into deep containers. A vision aid to raise or extend forward the line of sight of power WC users would be useful in many daily living, educational, and occupational activities. The design of the WC camera was based on the human factor requirements of a quadriplegic WC user and the results of a detailed House of Quality. The development of a pulley and belt-driven linkage system with a digital camera satisfied the top-ranked client and engineering requirements. Comprehensive engineering analyses were also performed to study the strength, safety, and failure modes of the WC camera mechanism. The WC camera provided a range of viewing positions from the front of the WC at eye level to more than 2 ft in front of the WC user’s knees at waist level. The solutions to expand visibility of WC users have not been adequately addressed in previous investigations in wheeled mobility.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Anthropometrical data put the average eye height of standing males to be 1.75 m. The average eye height of male power WC users is 1.20 m (1-2). In (a), the eye heights of someone standing, sitting in a wheelchair, and lying down are represented by top, middle, and bottom black dots. Lines of sights projected from these eye heights are shown. All three eye heights are possible by a nondisabled person; however, a WC user is restricted to viewing from a single sitting position height (middle black dot) that prevents seeing over objects or looking underneath standard height tables. (b) shows the extent WC users can lean forward to peer into or over objects. Standing persons can peer further because of their greater ability to lean forward and height advantage. In this example, the WC user cannot get closer to the container due to obstruction of the WC user’s footrests.

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Figure 2

The body mechanics of sitting in a WC makes forward viewing problematic because of their low height and the difficulty to direct one’s eye line at the object of interest. (a) A WC user attempts to peer inside a water bath on a cabinet-style laboratory bench. Without feet and knee clearance, (b) demonstrates the typical sideways posture of a WC user to get close enough to look inside a water bath on a hot plate. This posture can cause neck and back strain over time as well as safety concerns, such as positioning one’s face close to the hot water bath. (c) The WC camera permits viewing inside the water bath without having to strain the body to get near. Real-time camera viewing through a laptop PC also permits images and video to be recorded.

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Figure 3

Lateral view of the prototype WC camera mounted above the armrest of a power wheelchair. This location does not interfere with the movements of a WC user or the functions of the WC. When the device is retracted, the user is able flip up the armrests to transfer from and into the WC. In this view, the device is rotated 90 deg placing the digital camera slightly above eye height.

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Figure 4

Drawings of the individual link subassemblies are shown (a). Link 1 has a keyed hole through which a drive shaft transmits torque from the motor; on the opposite end of Link 1, there is a pulley screwed onto it with a bushing in the center. A threaded pin on Link 2 passes through the bushing on Link 1 and rigidly connects a pulley to Link 2. On the opposite end of Link 2 is a pulley screwed onto it with a bushing in the center. A threaded pin on Link 3 passes through the bushing on Link 2 and rigidly connects a pulley to Link 3. Finally, on the opposite end of Link 3 there is a bushing through which a threaded pin on Link 4 passes and rigidly connects a pulley to Link 4. (b) An assembly view of the device is shown with belts spanning the pulleys driving the rotation of the links.

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Figure 5

Five different positions of the WC camera are shown spanning a continuous range of the input link from 0 deg to 180 deg. These various positions are important for viewing in different situations.

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Figure 6

Free body diagrams are shown for each link in the mechanism

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Figure 7

The reaction torques transmitted between belts and pulleys as the input angle changed from 0 deg to 360 deg, though rotation past 180 deg was rarely performed for viewing purposes

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Figure 8

A close-up view of the mechanism showing the connection between Links 1 and 2. The pulley in the background attaches to and rotates Link 2 by the pin and nut. The pulley in the foreground is attached to Link 1.




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