Reverse Transfer Ball-Screw for Harsh Environments
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Solution Overview
Problem
Existing ball-screw assemblies in electro-mechanical actuators are prone to contamination and damage in harsh environments due to exposure of the threaded portion, leading to reduced service capacity and life.
Innovation Solution
A reverse transfer system ball-screw design featuring a nut and screw with complementary ball recesses forming an endless ball path, where the balls are continuously recirculated, protecting the screw threads and allowing axial movement of the rod relative to the nut, with additional features like helical recesses and cushions for deceleration and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the screw has a fully-threaded length to meet the linear translation stroke requirements, then the linear translation stroke is achieved, but the screw threads are exposed to contamination and damage in harsh environments
Solution Approach 1:
The patent inverts the traditional ball-screw configuration by placing the ball recirculation path in the nut rather than the screw. This allows the screw to be shorter and partially unthreaded, with the threaded portion protected inside the nut, while still achieving the required linear translation stroke through the ball recirculation mechanism.
Solution Approach 2:
The patent nests the ball recirculation path within the nut structure, with balls circulating inside the nut rather than externally on the screw. This nesting protects the threaded portions and balls from environmental contamination while maintaining the mechanical function.
2Reliability
If additional protective arrangements such as rod tubes or flexible covers are added, then the screw threads are protected from contamination, but the device complexity increases
Solution Approach 1:
The patent merges the protective function with the ball recirculation mechanism by integrating the ball path directly into the nut structure. The nut simultaneously serves as the protective housing and the ball circulation channel, eliminating the need for separate protective covers or tubes.
Solution Approach 2:
The nut is designed to perform multiple functions: it houses the ball recirculation path, protects the screw threads from contamination, and provides the mechanical interface for linear motion. This multi-functionality reduces the need for additional protective components.
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 solution effectively shields the screw threads from contamination, enhancing the service life and reliability of the actuator by ensuring continuous ball recirculation and controlled movement, while allowing for manual rotation in case of power failure.
Implementation Method 1
relative rotation between the nut and screw will cause the screw and rod to move axially relative to the nut
Data Source
AI summary
An electro-mechanical actuator (21) includes a reverse transfer system ball-screw (20). The actuator broadly includes a frame (22), a nut (43) mounted on the frame, at least one magnet (59) mounted on the nut, at least one coil (55) mounted on the frame, the coil being adapted to be selectively supplied with current to cause the nut to rotate within the frame, a rotary feedback device (80), and a screw (44) arranged within the nut for rotational and axial movement relative thereto. The screw and nut both have cooperative ball recesses (72, 74) that define a ball path in which a plurality of balls (73) are mounted. The ball recirculation path is provided in the screw. A rod (23) is connected to the screw for movement therewith. Relative rotation between the nut and screw will cause the screw and rod to move axially relative to the frame.