RESNA 27th International Annual Confence
DESIGN AND DEVELOPMENT OF A MANUAL WHEELCHAIR FOR INDIA
In 2000, the Indian government and the Artificial Limb Manufacturing Company (ALIMCO), the largest wheelchair manufacturer in India, established a relationship with the National Institute on Disability and Rehabilitation Research (NIDRR) and the Human Engineering Research Laboratories (HERL) to improve their wheelchair design. The result is a new manual wheelchair design. User needs, context of use and ALIMCO's manufacturing capabilities and cost bracket were considered as the basis for the design.
Many people in the United States and other “developed” countries still use wheelchairs that only barely meet their needs, but in India the number of people using inappropriate wheelchairs or none at all is enormous by comparison. According to conservative estimates, approximately 6% of India's population is disabled (approx. 60 million people). United Nations (UN) officials and other experts say the figure could easily be twice that. A large group percentage of these people (greater than 10 Million) have mobility disabilities. 1
These facts prompted the Indian government to seek collaboration with NIDRR and US wheelchair designers to improve the quality of their wheelchairs. The result has been a collaborative design project between HERL and ALIMCO since 2000.
ALIMCO is a governmental organization and currently the largest wheelchair manufacturer in South Asia, manufacturing (60,000) wheelchairs a year. ALIMCO exports products to many countries in the Mid-East and Asia. Major buyers of ALIMCO products are wheelchair dealers, non-governmental and governmental organizations. United Nations agencies like UNICEF and the World Health Organization have approved ALIMCO wheelchairs and use them in several programs.
The results of the ALIMCO-HERL relationship so far are ISO-ANSI/RESNA wheelchair testing and a new manual chair design. In 2001, representatives from HERL visited the Indian Spinal Injury Center and the ALIMCO manufacturing plant to establish the relationship and begin the design process. They informally evaluated ALIMCO's current wheelchair design, and established priorities for collaboration. In 2002 ALIMCO engineers visited HERL to further collaborate and attended the International Seating Symposium.
ALIMCO's current wheelchair design is primarily appropriate for hospital or short-term use. It does not meet the needs of the majority of wheelchair users who need a more lightweight, somewhat adjustable, comfortable, easy to maneuver, durable, reliable wheelchair. The goal of this project was to design such a wheelchair.
Three sets of criteria were considered when designing the new wheelchair; user needs, context of use and ALIMCO's cost bracket and manufacturing capabilities.
User needs considered during the design process includes the need for self-propulsion, variable posture support and transfers. Studies show that highly adjustable or custom wheelchairs are more comfortable and increase health for the user more than those less capable of being fitted to the user. 2,3 Additionally, a properly fitting wheelchair can help prevent the development of secondary disabilities, which can in some cases lead to death. One negative aspect of highly adjustable chairs is that they tend to have more components and can be heavier than those without adjustability. However, a moderately adjustable design was chosen because of its functionality and mass manufacturability.
Wheelchair collapsibility is another important user need. This is a necessary function for transportation on buses and strains, commonly used in India. Studies have shown rigid frame wheelchairs to be more durable than folding cross-brace chairs, but cross-braces can be strengthened by increasing the tubing diameter, changing tubing shape and by adding rigid plugs at the pivot point.
The average context of use in India differs from that of the United States. 1 Some of these differences are, rough unpaved terrain, less frequent maintenance and longer duration of use.
Studies using the ISO-ANSI/RESNA standards have shown that wheelchairs should be able to withstand a bare minimum of 200,000 double-drum cycles followed by 6,666 curb-drop cycles without a failure. This is equivalent to about 159 km (100 miles) of moderately rough terrain or 3-5 years of use. 4 Without an infrastructure of clinics, therapists, rehabilitation engineers and suppliers, wheelchairs in developing countries may not receive routine maintenance and broken chairs may not be easily replaced. Thus, wheelchairs designed for developing countries should be able to withstand more years of rough use than the average chair designed for a developed country, approximately 1,000,000 double-drum cycles and 66,666 curb-drop test drops, which is about the same as high quality manual wheelchairs used in industrial countries. ALIMCO's current wheelchair design only passed 67,799 double drum cycles before failing at the cross brace.
Components such as seat-backrest joints, cross braces and caster housing attachments have been identified as critical failure points in fatigue test results. 5 Thus, focusing on these components is important for designing a durable product.
ALIMCO's current market price is between $75-$125. The new design had to fall within this price range. The majority of ALIMCO's cost is materials, unlike US manufacturing where the majority of cost is labor. The new design maintains a low cost by using materials and processes currently used or readily accessible to ALIMCO.
Studies have identified important design features that accommodate user need; 2,3 adjustable axle position, caster alignment, seat dump, back rest angle and footrest height, light weight, accommodation to seating systems, and wheel and tire design. The new design incorporates these points of adjustability and a more efficient, lightweight geometry.
The final design is a folding cross-brace frame style in two adult sizes, 16x16 and 18x18 (seat depth x seat width). The leg rest angle is 60 degrees. There are 15 degrees of backrest angle adjustment from a vertical position. The seat dump can be adjusted from horizontal to seven degrees below horizontal by changing the axle position. The rear axle has eight possible positions ranging 3.75 inches front to back and 1.5 inches up and down. The caster angle can be adjusted ten degrees from vertical in order to keep the caster stem perpendicular to the ground. The footrests can be moved to three positions with a range of three inches.
Materials and manufacturing processes used in the chair include; bent welded mild steel tubing and two millimeter thick flat stock, aluminum sand castings, ALIMCO hand cycle bearings, rubber casters and bushings, turned brass bushings, non-structural plastic and stamped sheet metal. Pneumatic tires, rubber bushings at caster and axle attachment points and seat cushions increase shock absorption.
First the design team evaluated ALIMCO's most recent wheelchair design, assessing the quality of materials, quality of manufacturing, efficacy and usability of the design. Specific areas addressed include; weld quality and affected area, tubing strength, strength of fasteners, wheel rigidity/durability, bearing quality and housing design, seat material durability, frame construction and handgrip attachment.
Next, the team designed new frame geometry and built a prototype. The frame is 1020 steel alloy tubing, bent with a hand tubing bender and brazed together. The design team has built a prototype backrest adjustment, lightweight axle bracket and designed swing-away adjustable armrests, lightweight caster alignment bracket, lightweight adjustable footrests and anti-tippers. A lightweight-aluminum welding jig was also built. The jig has quick release v-blocks to hold the frame and cross-brace in place. Access holes in the jig plate allow for easy welding. Bearings allow the frame to be rotated in space.
The prototype chair was built for the purpose of testing the cross brace, frame durability and adjustable components. It survived testing on the double drum (200,000 cycles) and the curb drop (6,666 cycles). Once the final components are fabricated and tested a final India chair prototype will be constructed and tested to the ISO-ANSI/RESNA standards. Additionally, key components will be tested on a material-testing machine. Repeated loads will simulate actual use under the circumstance that we anticipate the wheelchair will experience during actual use.
The new India chair design is so far more durable and comfortable than the original ALIMCO chair. The true test of the design is how well the chair can be mass manufactured and how well it performs in the field.
The final prototype chair and aluminum quick-release welding jig will be delivered to India in 2004. Members of the HERL design team will then travel to India to discuss the prototype design and manufacturing issues as well as begin a dialogue about phase-two, wheelchair test equipment for ALIMCO. Future design work may include a children's tilt- in- space chair.
This project was funded by the NIDRR India Chair Supplement # H133E990001
180 Highland Drive
Pittsburgh PA 15206