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Very early in my career, I received a returned powerchair, the complaint being that it inexplicably slowed down.  When I reviewed the unit, the powerchair worked perfectly, and when we spoke with the provider and end user, they challenged my findings.  "Tilt the seat a bit, and you'll see," they instructed.

Indeed, tilting the seat slightly did slow the chair - which, again, proved my findings that the powerchair functioned perfectly, as designed.

What the provider and consumer didn't realize was that the powerchair's tilt seating system had an "inhibit," standard on virtually all power seating systems, which reduces speed, then locks out driving altogether, as a safety mechanism when the seat tilts. Education was the key to the repair, not parts.

If you have a tilt, recline, or elevating seat, you have likewise encountered "drive inhibits," maybe as unsuspectingly as my customer.  After all, inhibits are used on almost every power seating system, and since the means of inhibits are internal - and rarely discussed with consumers - it's understandable to be initially befuddled by their operation.  However, once inhibits are understood, they can be fully utilized to maximize safety, without limiting mobility.

Inhibits are simple in concept: When a power seat tilts, reclines, or elevates, a "switch" activates at a preset angle or height, and slows the powerchair's speed - namely, for safety reasons, as a tilt, reclined, or elevated seat is less stable than when in a typical driving position.  Some seating systems use a single inhibit mode - full speed up to 20-degrees, then full drive lock out, preventing any movement of the powerchair when the seat is fully tilted, for example.  Other systems use multiple inhibit modes - quarter-speed inhibit up to 4" of seat elevation, then full drive lock when the seats fully elevated.  Traditionally, there's no universal standard to at what point or speed an inhibit occurs - it varies from brand to brand of seating - but inhibits do occur in some form on almost all power seating systems.

Technologically, inhibits are found in four forms:  Mechanical, mercury, accelerometer, and inclinometer.  A mechanical inhibit is a simple switch that is activated based on the seat's movement - that is, the seat's movement triggers a switch, activating the inhibit.  A mercury switch is based on the movement of fluid, shifting the mercury as the seat tilts, which triggers an inhibit.  And, an accelerometers or inclinometer is within a powerchair's electronics, a sort of artificial intelligence that senses the seat's movement and angle, setting the inhibit at the preset stage.  There's no single inhibit technology that's more common or ideal than others, as all are successfully used, and the application of where a manufacturer wishes to place the inhibit device - in the actuator, seat frame, or electronics - dictates the technology used.

For some consumers, inhibits can prove frustrating, as with being unable to maneuver when tilted or elevated within one's home.  While inhibits are a clear safety feature toward dynamic stability, they can be adjusted if a provider is comfortable performing an alteration for a responsible, prudent consumer.  Specifically, mechanical and mercury switches can be mechanically adjusted to go into inhibit at later points, and through electronic means, including accelerometers and inclinometers, inhibit angles and speeds are adjustable via programming.

Ultimately, inhibits are a great technology, preventing unknowing consumers from underestimating the dynamics that power seating can add to a powerchair's center of gravity when tilted, reclined, or elevated.  Sure, when you're tilted, and the phone across the room rings, inhibits are a tad irksome, having to reposition your seat before moving.  However, inhibits are somewhat flexible, and if there's a valid reason why one needs an inhibit adjusted, providers can help with best tailoring a system.  

Maybe inhibits aren't so inhibiting, after all.

Published 4/07, Copyright 2007,