Person Support Pivot Assembly with Moving Virtual Axis to Reduce Shear
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Solution Overview
Problem
Person support apparatuses, such as beds and recliners, often introduce shear forces on patients when the backrest pivots relative to the seat, causing discomfort due to mismatched pivoting motions between the back and hips.
Innovation Solution
A pivot assembly that creates a virtual pivot axis, shifting the backrest backwards and upwards as it pivots, reducing shear forces by allowing the backrest to pivot with respect to the seat about a moving axis that changes position based on the backrest's orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the backrest pivots relative to the seat in a conventional manner, then the backrest can change position, but shear force is introduced against the patient's back causing discomfort
Solution Approach 1:
The patent applies the dynamics principle by creating a moving virtual pivot axis that changes position as the backrest pivots. Instead of a fixed pivot point, the virtual pivot axis moves along an arc path, allowing the backrest to follow a curved trajectory that better matches the natural motion of the patient's back relative to their hips. This dynamic adjustment eliminates shear forces while maintaining smooth backrest positioning.
2Object-affected harmful factors
If a pivot assembly is designed to reduce shear forces through a moving virtual pivot axis, then patient comfort is improved, but the mechanism may occupy more space and use more material
Solution Approach 1:
The patent segments the pivot assembly into multiple independent components: a backrest slide bar that moves along the backrest, a seat slide bar that moves along the seat, and linkages connecting them. This segmentation allows each component to perform a specific function in creating the moving virtual pivot axis, achieving shear force reduction while keeping individual components compact and the overall assembly space-efficient.
3Device complexity
If the backrest and seat pivot with fixed geometry, then the mechanism is simple and uses less material, but it cannot match the pivoting motion of the patient's back
Solution Approach 1:
The patent introduces intermediary elements (the slide bars and linkages) that mediate between the fixed geometric constraints of the backrest and seat and the dynamic requirements of patient comfort. These intermediaries create the moving virtual pivot axis that adapts to match the patient's back motion, bridging the gap between simple fixed geometry and complex adaptive motion.
Data Source
AI summary
A person support apparatus includes a support surface for supporting a person thereon. The support surface includes at least a seat and a backrest coupled together by a pivot assembly. In some embodiments, the pivot assembly includes a backrest slide bar mounted to the backrest and a seat slide bar mounted to the seat. The backrest and seat slide along their respective slide bars when the backrest pivots. A seat link is coupled to the seat and backrest slide bar, and a backrest link is coupled to the backrest and seat slide bar. The slide bars are coupled at their ends to each other. The pivot assembly creates a virtual pivot axis that, as the backrest pivots from an upright position to a reclined position, moves backward and upwardly. Elongate openings may be defined in the slide bars to support the slide bars on the seat and backrest, respectively.