RSS Feeds
Gas spring gives grandma bounce
By John Day, Contributing Editor -- Design News, September 18, 2000
Ft. Collins, CO —Jon Workman, an engineer at UltiMedCo, wanted to help his grandmother. She used a collapsible walker for mobility, but arthritis in her hands made it painful to grasp the walker's handrails.
UltiMedCo manufactures assistive and adaptive devices to aid rehabilitation. So Workman decided to design a product that could replace the walker and give his grandmother more mobility and freedom. The result is the TheraTrek 1000 gait trainer and mobility device.
Gait trainers improve mobility or develop ambulating skills for people experiencing problems with balance or muscle control. But most gait trainers are manufactured from steel tubing, and require some use of a person's hands or arms. Workman designed the TheraTrek 1000 out of lightweight, heat-treated aluminum that supports the user through the pelvis, thus freeing the upper body for normal use.
The user or a therapist can determine the amount of weight supported by the feet while allowing the TheraTrek to support the rest of the user's body (up to 250 lb). In an upright position, the user can extend her or his legs to the floor and "walk." For user convenience, the trainer fits in a car trunk and weighs no more than a standard wheelchair.
Given the demands on height adjustment, weight-bearing requirements, and flexibility, Workman decided to use an elastic Bloc-O-Lift (gas spring manufactured by Stabilus (Gastonia, NC) in the gait trainer. The gas spring is part of a four-bar linkage that connects the gait trainer's base frame with the pelvic support system and cradle.
The TheraTrek also has a unique cable assembly, supplied by Cable Manufacturing and Assembly Company (Bolivar, OH), to adjust the gas spring from two locations on the device. According to UltiMedCo's Ken House, the cable release gas spring allows the unit to be collapsed easily for shipping and portability. The gas spring also permits the pelvic support system to raise and lower to an ideal height.
The natural feel of the device provides a realistic walking motion. The elastic locking gas spring provides some vertical motion to replicate the "bounce" of unaided walking. Stabilus also adjusted the orifice in the piston, which affects the dampening rate. This was tuned to control the rate of movement when the actuation lever is moved.
If the user slips, the locking cylinder reacts softly to prevent a fall. The soft bottoming of the cylinder prevents a sudden stop, which would be painful. The TheraTrek then gently rebounds to the preset height.
The gas spring is connected through two cables to levers on either side of the device's cradle. The levers control cylinder actuation and allow adjustment of the Bloc-O-Lift stroke to customize weight bearing and height. This patented control system allows either hand to make adjustments.
"We first tried a fixed-height setting, but that was uncomfortable and unnatural," House recalls. "Next, we tried adding elastomeric bands, but the system was difficult to control."
Stabilus then suggested that the team try a spring blocking gas spring. "This proved to be the answer," says House. "All we needed then was to have Stabilus adjust the gas pressure of the device to optimize the performance."
Talkback
DN's Resource Center Get Free Information, Made Easy
-
Understanding a Modular Instrumentation System for Automated Test
National Instruments | White Paper
Request Item -
Advanced Features of High Speed Digital I/O devices : White Paper Series
National Instruments | White Paper
Request Item
