Automatic locks safeguard wheelchair occupants

Marion, LA--Some patients in wheelchairs, particularly the elderly, have a tendency to fall and injure themselves when trying to stand. The problem: They don't engage their wheelchair's manual locks.

Confronted with this problem after visiting patients at nursing homes, physician Grady Dugas came up with the solution--brakes that automatically engage as soon as the wheelchair occupant starts to get up.

Dr. Dugas' patented invention works like this: When weight is removed from the seat of a chair fitted with his "Safer" automatic locks, spring-energized levers rise, shifting fixed gear blocks into contact with gear hubs mounted on each wheel. Teeth on the blocks and hubs mesh to prevent the wheels from turning.

Handle-mounted overrides disengage the locks in order to allow attendants to roll an empty chair. And the locks don't interfere with the ability to fold the chair for storage or transport.

The right materials played an important role in making the design not only feasible, but cost-effective. For example, the lock system for a typical chair uses various nylon Zytel(reg) resins for 24 parts (12 on each wheel), supplied by DuPont Engineering Polymers (Wilmington, DE).

In the case of the gear blocks and override handles, a 33% glass-reinforced formulation, Zytel 70G33L, provided the needed high stiffness, strength, and toughness. For gear hubs, seat paddles, override clamps and stabilizer hooks, a toughened, unreinforced grade, Zytel(reg) 3189, provided the right degree of toughness and flexibility.

For all remaining nonmetal parts, the molder, United Plastic Molders (Jackson, MS) used a 50/50 blend of the two grades to achieve an intermediate level of stiffness.

"DuPont engineers suggested blending the two grades," says Bill Hoge, United Plastic Molders president. "The technical support proved very helpful in the development process. All in all, Zytel allowed us to engineer a lock that provides outstanding durability, good looks, and low maintenance, while adding little weight to the chair."

The molder not only helped develop the design, but made the tooling for the locks. Following the device's successful debut, Hoge and Dugas formed Safer Wheelchair Wheel Locks Inc.

The locks come in ready-to-install kits for retrofitting to many leading wheelchair models. They will work with other locks already installed. Installation takes anywhere from 20 minutes to an hour based on the experience of the installer, according to Dr. Dugas. Cost: $110 to $140 depending upon the quantities sold and the model of wheelchair.