Flexible Pivot Structure for Large-Angle Rotation With Low Center Shift
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Solution Overview
Problem
Conventional flexible pivots for space applications suffer from significant center shift issues at large angles of rotation, leading to accuracy degradation and compatibility problems between ground and orbital conditions, due to reduced stiffness and increased axial stresses, which complicates the use of accurate angular sensors and motor implementation.
Innovation Solution
A flexible pivot design featuring concentric rings with angularly homogeneous flexible legs, utilizing V-shaped joining members that allow the legs to flex without tension, maintaining their length and original stiffness, and enabling rotation up to ±40° in each direction without altering radial or axial stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the rotational range is increased by increasing the diameter and length of the flexible legs, then the rotational range is improved, but the radial and axial stiffness is lowered
Solution Approach 1:
The flexible pivot is segmented into multiple flexible legs (at least three) arranged angularly homogeneously around the central axis. Each leg is independently connected to the first and second rings, allowing the structure to achieve large rotational ranges while maintaining stiffness through the collective action of multiple segmented elements rather than relying on a single long leg.
Solution Approach 2:
The flexible legs are designed with specific local geometric properties including a straight portion and an inclined portion with different cross-sectional dimensions. The inclined portion has a smaller second moment of area than the straight portion, creating localized flexibility zones that allow rotation while maintaining overall structural stiffness. This local quality differentiation enables the legs to flex appropriately during rotation without compromising radial and axial stiffness.
2Measurement precision
If three blades are implemented at 120° arrangement with cutting at the center or linear flexibility at the root to achieve theoretical zero center shift, then the center shift is improved, but the axial and shear stiffness is reduced
Solution Approach 1:
The flexible legs incorporate both straight and inclined portions that dynamically adapt their flexibility characteristics during rotation. The straight portion maintains high stiffness to prevent center shift, while the inclined portion with reduced second moment of area provides necessary flexibility for rotation. This dynamic structural design allows the pivot to maintain near-zero center shift while preserving adequate axial and shear stiffness.
Solution Approach 2:
The flexible legs are constructed as composite structures with different geometric sections (straight and inclined portions) having different mechanical properties. The combination of these composite sections creates a leg that simultaneously provides the stiffness needed to minimize center shift and the flexibility needed for rotation, resolving the contradiction between precision and stiffness.
3Length of moving object
If the flexible legs are made longer to increase rotational range, then the rotational range is improved, but the axial stresses increase reducing fatigue life
Solution Approach 1:
The flexible legs feature localized flexibility zones in the inclined portions with reduced second moment of area, concentrating the flexing action in specific regions rather than distributing it throughout the entire leg length. This local quality approach allows the legs to be sufficiently long for large rotational ranges while minimizing axial stresses in the critical root regions, thereby preserving fatigue life.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design minimizes center shift, maintains original stiffness, and allows for precise and extended rotation, enhancing the accuracy and reliability of angular sensors and motor implementation in space applications by avoiding tension and maintaining the original radial and axial stiffness.
Implementation Method 1
a plurality of flexible legs (3.1, 3.2 and 3.3) associated to both rings (1, 2), one end of each flexible leg (3.1, 3.2 and 3.3) being associated to the first ring (1) and the other end of each flexible leg (3.1, 3.2 and 3.3) being associated to the second ring (2)
Data Source
Figure 1
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Figure 3
AI summary
A flexible pivot (100) comprising a first ring (1), a second ring (2), and a plurality of flexible legs (3.1, 3.2, 3.3) associated to both rings. The rings are concentric, the second ring being rotatable in respect of a central axis (0) of both rings. The flexible legs are arranged in series in the axial direction, one end of each flexible leg being attached to the first ring and the other end being attached to the second ring, such that with the second ring in a rest position, each flexible leg forms a straight line passing through the central axis. The flexible pivot comprises a V-shaped flexible joining member (41, 42) for connecting each end of each flexible leg to the corresponding ring.