Linear Actuator Backup Load Path With Visual Failure Indication
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Solution Overview
Problem
Existing linear actuators lack clear indications of primary or backup component failures, making it difficult to determine if primary or backup components have failed, which can lead to operational issues in critical applications like aircraft systems.
Innovation Solution
The design incorporates a housing, ball screw, tie rod, friction springs, and a bearing with an interference fit, allowing for a primary load path and secondary load paths to maintain functionality and provide visual failure indications through a gap closure mechanism in case of component failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single load path is used in the actuator, then the structure is simple, but the reliability is reduced because there is no backup path when primary components fail
Solution Approach 1:
The patent pre-configures secondary load paths (through friction springs and bearing assemblies) that are ready to engage before any failure occurs. The friction springs are pre-loaded against the ball screw and tie rod, and the bearing assemblies are positioned to automatically take over load transmission when the primary ball screw-tie rod connection fails, eliminating the need for complex detection and switching systems.
Solution Approach 2:
The friction springs provide a pre-established backup mechanism that can absorb and transmit loads immediately upon primary component failure. The springs are pre-compressed between the ball screw and tie rod, creating a cushioning effect that prevents sudden load drops and maintains actuator functionality without requiring complex active control systems.
2Difficulty of detecting and measuring
If no visual indication mechanism is added, then the device complexity remains low, but the difficulty of detecting and measuring component failure increases
Solution Approach 1:
The patent employs visual indication through the presence or absence of a gap that can be observed during inspection. When the actuator is properly assembled and functional, a specific gap is visible between components; when failure occurs, this gap changes or disappears, providing an immediate visual cue of the failure state without requiring electronic sensors or complex indication systems.
3Strength
If interference fit is used between bearing and tie rod, then the connection strength increases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise interference fit parameters (e.g., 0.0015 to 0.0030 inch interference) that balance connection strength with manufacturability. By carefully controlling the interference magnitude, the design achieves sufficient mechanical strength while remaining compatible with standard manufacturing tolerances and assembly processes.
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
This configuration ensures continued operation and provides visual indicators of failure, ensuring reliable performance and maintenance in aircraft systems by diverting loads through secondary paths and maintaining connection with the aircraft structure.
Implementation Method 1
a bearing (26) that may be interference fit with the tie rod (16) and clearance fit with the ball screw (14)
Implementation Method 2
a plurality of friction springs (20, 22) in the ball screw (14) and around the tie rod (16)
Data Source
AI summary
An actuator may include a housing, a ball screw engaged with the housing, a tie rod disposed in the ball screw, a plurality of friction springs in the ball screw and around the tie rod, and a bearing having an interference fit with the tie rod and a clearance fit with the ball screw.