April/May 2000

Advanced Seating Systems:

By Rory A. Cooper, PhD; Mark R. Schmeler, MS, OTR/L, ATP; Rosemarie Cooper, MPT; and Michael L. Boninger, MD

New mobility product designs, robotics technology, and wheelchair accessories bring better options for people with disabilities.

There have been several recent advances in wheelchair technology that could bring greater mobility for people with disabilities and for geriatric clients. These advances depend on the proliferation of computing technology (both hardware and software) and developments in materials and their manufacturing processes. The new mobility product designs and the commercial experimentation with robotics technology for personal mobility are both exciting.

Hybrid systems (combination of manual propulsion and electric-powered assist) and robotic systems (dynamic stabilization and transformation) represent significant advances in electric-powered mobility.

Hybrid systems. There are several hybrid systems under development. Applying a torque to the pushrims of the wheelchair activates the device. The pushrim torque is regulated by sets of linear compression springs and recorded by a simple potentiometer that senses the relative motion between the pushrim and hub. The potentiometer signals from both wheels are interfaced to a microcontroller. The microcontroller algorithm coordinates control of each wheel’s DC motor. The software simulates inertia, allowing for a coast, compensates for discrepancies between the two wheels (eg, differences in friction), and provides an automatic braking system activated when applying a reverse torque to the pushrims. The system is powered by a single custom-designed nickel-cadmium or nickel-metal-hydride battery. The wheels have quick-release axles. The entire unit has a mass of about 10 kg, and a range of about 12 km on a single charge.

Robotic systems. Many environments such as stairs, high curbs, steep ramps, high objects, soft surfaces, and uneven terrain are not accessible using a wheeled mobility device. Performance compromises are numerous and must be considered for each individual. Robotic systems are electronically stabilizing devices, providing the opportunity to enhance mobility without some of the traditional compromises. By incorporating state-of-the-art software and hardware, they respond to changes in terrain. This permits the systems to be used to traverse nonuniform surfaces and steep inclines, climb curbs, and negotiate some stairs.

The mobility system is based on a chair mounted through linkages to a wheeled base. Robotic systems have four primary wheels, each controlled through its own electric motor, and two caster wheels. The two sets of drive wheels on either side of the chair form a cluster. Each cluster may rotate about its central axis while the wheels may rotate about their hubs. This provides the system with more degrees of freedom than an electric-powered wheelchair. It is operated by a set of central custom computers that help maintain stability and provide the user with control. Robotic systems incorporate a variety of sensors for attitude control, speed control, self-diagnosis, and changing operational functions. They are operated via a hand-controlled joystick and a user panel containing several switches.

There are a multitude of options when selecting a wheelchair and seating system. It is important to understand that there is no one universally ideal intervention to meet all needs as in the one-size-fits-all approach commonly seen in some practices.

Durability studies have shown that ultralight and lightweight wheelchairs, although more expensive in cost initially, are actually less costly to operate in the long term besides being more comfortable, easier to propel, and more adjustable. The outcomes of these and other research studies need to be carefully considered from a long-term, cost-benefit perspective when prescribing wheelchair seating and mobility interventions. Clinicians also have the responsibility of learning about these innovations and findings in order to justify and advocate to funding sources as well as policy makers to ensure that their clients are provided with the most appropriate and reasonable interventions.

Manual Wheelchair Accessories

The availability of accessories for wheelchair riders has expanded significantly over the past few years. The wheelchair rider most likely will choose or select an accessory based on personal abilities, activities, skill level, and personal preference. The selection of certain accessories might vary as the needs and the skill level of the wheelchair rider change. By keeping up to date on the current availability of accessories, users can update their wheelchairs to achieve optimal performance.

Decrease in maintenance can be achieved by:

• Airless tire inserts. Flat-free inserts are made out of foam and designed to fit inside the tire to eliminate the risk of a flat tire. The disadvantage is that the ride is rougher than with air-filled tires and it is more difficult and expensive to replace the tires when they wear out.

• Quick-release axle pins. Attachment of both rear wheels via quick-release pins allows for quick wheel montage without tools. This is beneficial in stowing the wheelchair, especially in a car. Protection of clothing can be achieved by:

• Armrest panels. Made from metal or plastic, the panels are designed to attach to the armrest assembly, between the wheel and the rider. This helps keep the tire dirt outside of the armrests and away from clothes. The disadvantage is that it may reduce the effective width of the wheelchair seat and may cause pressure on the hip bones.

• Clothing guards. Mud guards are made out of plastic or nylon and are designed to stay between the wheels and clothes to keep clothing from getting soiled by dirt kicked up from tires. The disadvantage is that they may narrow the width of the seat. Safety can be compromised by a higher risk of falling out of the chair or tipping the chair; increased likelihood of inability to control the chair on an incline; losing control during transfers, and an inability to control legs and feet. Safety, to prevent falling out of the chair, can be achieved by:

• Chest straps, shoulder harnesses, and lap belts. Depending on the wheelchair riders’ limitations, these accessories can prevent injury that might occur when the user falls forward out of the wheelchair due to sudden stops. The disadvantage is that these devices lock the rider into the wheelchair, which may cause injury if the chair tips completely forward. In addition, they may limit reach. Safety, to prevent tipping the chair, can be achieved by:

• Antitippers. These small wheels attach to the front or back of the wheelchair and are designed to prevent the chair from tipping over forward or backward. They may allow the rider to climb steep hills without tipping backward. The disadvantage is that, with the antitippers attached, the rider cannot balance in a wheelie, and they limit the ability to cross thresholds and climb obstacles and curbs. Safety, to prevent inability to control the chair on an incline, can be achieved by:

• Hill climbers. Grade aids attach to the wheelchair on or near the wheel lock. When engaged, they allow the wheelchair to roll forward and reduce the likelihood of rolling backward on an incline. The disadvantage is that the device may interfere with usual wheelchair propulsion. Safety, to prevent loss of control during transfers, can be achieved by:

• Caster-pins/caster-locks. Pins lock the casters in the forward or rearward trailing position, which stabilizes the wheelchair during transfers. They are helpful to those new to using a wheelchair.

• Wheel locks. They are designed to prevent a stationary wheelchair from rolling. The disadvantage is that they may interfere with propulsion and add weight. Safety, to prevent the inability to control movement of the legs and feet, can be achieved by:

• Foot straps and leg straps. Attached to and above the footrests are straps, designed to prevent the feet from falling off the footrests, therefore reducing the chance of injury or accident if the feet hit the ground in front of the footrest. They can also prevent the legs from falling onto the face in a backward fall. Ease in carrying and transporting objects can be achieved by:

• Fold-down briefcase rest ledge that attaches to the footrest side rails. When unfolded, the rest ledge can hold a briefcase or travel bag at the feet, where the user can access it easily. It folds up and out of the way when not in use. The disadvantage is that a heavy bag may tip the wheelchair forward.

• Seat pouch. A pouch like a fanny bag that is attached under the wheelchair seat. The disadvantage is that people with little or no upper strength may have difficulty reaching under-seat pouches.

• Web-cradle. This square piece of mesh attaches below the seat and is used for storage. The disadvantage is that the stored items may get dirty. Ease in driving/propulsion can be achieved by:

• Pushrim-activated power-assisted wheelchair (PAPAW). This wheelchair is designed to ease manual propulsion by amplifying the rider’s propulsion force, much like the power steering of a car. It is designed to decrease the propulsion effort of the wheelchair rider and to reduce the force on the wrist, elbow, and shoulder joints, which may reduce the risk of repetitive strain injuries caused by long-term, manual wheelchair propulsion.

• Add-on power system. This system is designed to convert a manual wheelchair into a powered system. This device can provide assistance when required, while still permitting the chair to be used in manual mode. The disadvantage is the added weight decreases the maneuverability of the wheelchair in manual mode. Increase in convenience to be achieved by:

• Travel wheels. These two caster wheels are designed to attach to the low-back frame of the wheelchair. When quick-release rear tires are removed, it allows the rider to pull him/herself through a narrow door or down an airplane aisle.

LOOKING FOR EXPERT ADVICE? Experts here are available to answer all your questions! Please contact us for more information about this feature, or to become an expert.

MEDIA CENTER Interactive Media  Archives  · November 2008  · October 2008  · August/September 2008  · Fall 2008 Product Directory  · July 2008  · June 2008  · May 2008  · April 2008  · March 2008  · January/February 2008  · All Archives  Newsletter  · Rehab Today Resources Classifieds Calendar Consumer Resources Media Kit Advertiser Index EAB Reprints Submit an Article