The content of this article is a contribution of Free Wheelchair Mission
Background
ISO 7176 contains a family of tests that have proven valuable for decades. These tests are used to establish the adequacy of a wheelchair design, meaning is it strong, stable and durable. Many government agencies and commercial companies believe that if a wheelchair satisfies ISO 7176 requirements, it can be sold and used in developed countries. For wheelchair users in developing countries, ISO 7176 is a good starting point, but there is need for more rigorous testing. How do we know this? Because wheelchairs that pass ISO 7176 can lose their utility in a matter of months when faced with the terrain commonly found in developing countries.
Purpose
Our goal was to develop a machine that would more closely simulate a developing countries terrain, allow multiple wheelchairs to be tested at one time, and provide consistent, reproducible results
Principle
ISO 7176 is intended to test a single wheelchair. It is a pass/fail kind of test. It was not intended to be a convenient tool for developing of a new wheelchair design, or for optimizing an existing design. Yes, one can and some do run portions of ISO 7176 for extended periods of time to a point of wheelchair destruction. One difficulty comes from comparing results from one wheelchair to results from a control sample run at a different time. Many researchers test individual components of a wheelchair and gather meaningful results. Often, at least in our hands, an individual part isolated from the wheelchair assembly may behave quite differently. What seemed to be lacking in this arena is a way to test a test wheelchair against a control standard wheelchair on a machine that will provide reproducible results.
Apparatus
After considerable searching, we came up with a concept of a machine running a conveyor belt. We attach obstacles on a conveyor belt, and immobilizing wheelchairs on top of this conveyor belt. Our belt is 5 feet wide and about 40 feet long. The machine has four test stations about 6 feet apart. We developed a way to attach a wheelchair that simulates the situation when a user is propelled by an attendant. In distinction to a double drum test, the wheelchair is not constrained in the transverse or in forward-backward direction. By doing this, we much more closely simulate the actual conditions a wheelchair and user encounters in actual use.
We started by mounting ridges identical to those detailed in ISO 7176 for the double drum. We can adjust the speed of the conveyor belt from 0 to 5 MPH. We chose 2.33 mph to be the equivalent to the speed of the double drum, and we made the spacing between the ridges to be as they are in the double drum. We simulate the curb drop in a much more realistic manner with a three-piece ramp about 2 feet long with a vertical drop of 50 mm to be the same as the curb drop test. We run this machine 24/7. It is outfitted with optical sensors between the four wheelchair stations. These sensors stop the conveyor belt if a part falls of the wheelchair. We have an optical curtain on the catwalk. This optical curtain is an OSA safety requirement. It immediately halts the conveyor belt if someone were to try to walk on it during its operation. If a test is interrupted for any reason, we receive an email notification. Four video cameras will show us what caused the interruption.
We add strain gages and accelerometers to various parts of wheelchairs and are hoping someday to be able to use the data we collect to identify weaknesses in a wheelchair design before destruction occurs. We are very excited about testing wheelchairs designed or purchased by peer groups focused on this unmet need of 70 million wheelchairs in the developing world.
As far as the usefulness of LOTUS, during these past two years we have increased the time to failure of our GEN_2 wheelchair 35 times!
We call this machine LOTUS, after a girl in India who learned how to walk after we provided her with a wheelchair.
Additional information include:
- Video of the LOTUS in operation.
- Paper presented at ISS 2019. See Downloadable Files.
- Full set of Solidworks drawings for anyone wishing to duplicate LOTUS provided upon request. LOTUS was designed and manufactured for Free Wheelchair Mission by RPM and Associates of Rapid City, South Dakota. LOTUS was designed to be shipped on a flat bed truck (or container). There are no welds. It can be disassembled and moved. Everything bolts together. We estimate it will cost about $60,000 to duplicate.
Acknowledgements
Don Schoendorfer from Free Wheelchair Mission for collaborating with the content and documentation for this article.
