Reducing back displacement in the powered reclining wheelchair.

The powered reclining wheelchair used by quadriplegic and other severely disabled people was studied to determine how the chair could be modified so that repeated recline would not produce shear forces that tend to cause the user to be relocated in the chair, limiting independent functioning. Three modifications of the chair were studied: a freely sliding back, a commercially available powered sliding seat, and 4-bar linkage to hinge the chair back. A counterbalanced, freely sliding back was constructed for testing and was instrumented to measure displacement of the person in the chair during recline. The curves of back displacement vs angle or recline were determined for a sample or 8 quadriplegic subjects. The sliding back mechanism was determined to be impractical for incorporation into current chair designs since it required a heavy, rigid back frame. The sliding seat was found to have limited value since it only slightly decreased the back motion during recline. However, the 4-bar linkage virtually eliminated relative motion between the person's back and the chair back, providing a mechanism for potentially resolving this problem both in new recliner design and for retrofit to existing reclining wheelchairs.