Inverted Roller Screw Actuator for Stiff Flight Control Surfaces
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Solution Overview
Problem
Long stroke ball screw actuators used in aerial vehicles have low stiffness and natural frequencies, leading to increased weight and complex maintenance due to the large diameter output rod and ball screws.
Innovation Solution
An actuator system featuring an inverted roller screw with a shaft, rollers, and an inverted nut, where the nut includes a lubricant source and distribution channels to supply lubricant to the rollers, reducing wear and maintenance complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If larger diameter output rod and ball screws are employed to increase stiffness and natural frequency, then stiffness and natural frequency are improved, but weight increases and space requirements increase
Solution Approach 1:
The patent inverts the traditional ball screw configuration by placing the nut on the stationary side and the screw on the moving side. This inversion allows the use of a smaller diameter screw while maintaining stiffness requirements, thereby reducing weight without compromising structural integrity or natural frequency performance
2Strength
If larger diameter output rod and ball screws are employed to increase stiffness and natural frequency, then stiffness and natural frequency are improved, but device complexity and maintenance requirements increase
Solution Approach 1:
By inverting the ball screw configuration, the patent simplifies the overall device architecture. The stationary nut eliminates the need for complex sealing and lubrication systems on the moving rod, reducing maintenance complexity while achieving the required stiffness through optimized screw geometry
Solution Approach 2:
The patent extracts the lubrication and sealing requirements from the moving output rod by placing the ball screw mechanism inside the stationary actuator housing. This separation removes complex maintenance-related components from the moving assembly, simplifying the overall device structure
3Length of moving object
If long stroke ball screw actuators are used, then stroke length is achieved, but natural frequency decreases
Solution Approach 1:
The inverted configuration allows the screw to rotate within the stationary nut, enabling long stroke lengths to be achieved through multiple rotations without requiring an excessively long screw diameter. This maintains the natural frequency by keeping the screw diameter compact while achieving the required stroke through rotational motion
Solution Approach 2:
The patent utilizes the dynamic rotation of the screw within the stationary nut to achieve long stroke lengths. By allowing the screw to rotate multiple times within a compact diameter, the system achieves extended stroke without compromising the natural frequency, as the critical dimension remains the screw diameter rather than the stroke length
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 actuator system achieves reduced weight and simplified maintenance by utilizing the inverted roller screw and lubrication system, while maintaining sufficient stiffness and natural frequency for flight control surfaces.
Implementation Method 1
The inverted nut includes a source of a lubricant in fluid communication with the inner bore and the plunger is configured to be received within the inner bore to supply the lubricant to the at least one roller
Data Source
AI summary
An actuator system for a flight control surface of an aerial vehicle includes a shaft. The shaft includes at least one roller to rotate with the shaft and a plunger. The at least one roller includes a plurality of roller threads. The actuator system includes an inverted nut defining an inner bore including a plurality of nut threads. The inverted nut is coupled about the shaft such that the plurality of nut threads are to engage with the plurality of roller threads to move the inverted nut relative to the shaft. The inverted nut includes a source of a lubricant in fluid communication with the inner bore and the plunger is to be received within the inner bore to supply the lubricant to the at least one roller.