Ball Screw Linear Actuator Structure for Grease Retention
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Solution Overview
Problem
In linear actuators, the existing rotation stopper design allows grease to easily flow out of the nut due to a large gap between the nut's edge and the cylindrical portion, leading to grease accumulation and reduced screw shaft protrusion, necessitating the return of a large amount of grease from the edge of the opening portion to the inside of the nut during screw shaft retraction.
Innovation Solution
A linear actuator design featuring a screw shaft with a male spline portion and a step surface, a nut with a first opening portion and first stopper, and a piston with a cylindrical portion that abuts the step surface, reducing the gap between the nut's edge and the cylindrical portion, preventing grease outflow, and ensuring grease returns to the nut during retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a swelling portion is provided at the base of the protrusion of the second stopper to increase rigidity, then the protrusion is not damaged even when a large load is input, but the gap amount between the edge of the opening portion and the cylindrical portion increases, causing grease to easily flow out
Solution Approach 1:
The second stopper is divided into two separate components: the protrusion (for providing rigidity and load resistance) and the cylindrical portion (for minimizing gap and preventing grease outflow). This segmentation allows each component to fulfill its specific function without compromising the other, resolving the contradiction between rigidity and grease retention.
2Loss of substance
If the gap amount between the edge of the opening portion and the cylindrical portion is reduced to prevent grease outflow, then grease retention is improved, but the cylindrical portion may come into contact with the inner peripheral surface of the nut, increasing friction
Solution Approach 1:
The cylindrical portion is designed with a specific diameter that is larger than the groove bottom of the outer peripheral raceway surface but smaller than the inner diameter of the nut. This local dimensional specification creates an optimal gap that prevents grease outflow while avoiding contact with the nut's inner peripheral surface, thus eliminating friction.
3Loss of substance
If the cylindrical portion has a larger diameter to reduce the gap and prevent grease outflow, then grease retention is improved, but the cylindrical portion may contact the inner peripheral surface of the nut during operation
Solution Approach 1:
The diameter of the cylindrical portion is precisely controlled within a specific range: larger than the groove bottom of the outer peripheral raceway surface but smaller than the inner diameter of the nut. This parameter optimization ensures that the cylindrical portion is close enough to the opening portion edge to prevent grease outflow, yet far enough to avoid contacting the nut's inner peripheral surface during rotation.
Data Source
AI summary
A linear actuator of the present disclosure includes a ball screw device, a piston, and a rotation stopper. A screw shaft includes a screw shaft body, a male spline portion, and a step surface. A nut includes a first end surface, a first opening portion, and a first stopper. The piston includes a piston body, a cylindrical portion having a cylindrical shape, protruding in a second direction from a central portion of an opposite surface, and fitted into the male spline portion, and a second stopper protruding in the second direction from the opposite surface. The first stopper and the second stopper abut on each other and form the rotation stopper when the screw shaft is at an initial position. The step surface is arranged in the second direction compared to the first opening portion and is located inside the nut when the screw shaft is at the initial position.