Ball-screw spline with internal ball return path
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Solution Overview
Problem
Conventional ball-screw splines require a longer spline shaft due to the projection of the return tube, limiting the movement of the spline nut and resulting in an oversized electric actuator.
Innovation Solution
A ball-screw spline design where the ball-screw nut has an integral screw and extended portion with a ball return path integrated into the inner surface, allowing the balls to circulate without projecting from the outer surface, enabling the spline nut to move over the entire length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return tube projects from the outer peripheral surface of the spline shaft to return balls, then the infinite circulation path is formed, but the spline nut cannot move over the entire length of the spline shaft, requiring a longer spline shaft and resulting in upsizing of the electric actuator
Solution Approach 1:
The ball return path is nested within the inner peripheral surface of the screw shaft, with the return tube positioned inside the hollow portion rather than projecting outward. This nesting arrangement allows the ball circulation system to be contained within the existing structure, eliminating the need for additional length while maintaining the infinite circulation function.
Solution Approach 2:
The ball return path is repositioned from a radial projection (extending outward from the outer surface) to an axial arrangement (within the hollow portion along the axial direction). This dimensional change allows the ball circulation system to utilize the internal hollow space rather than occupying external radial space, thereby reducing the overall length requirement of the spline shaft.
2Ease of operation
If the return tube projects from the outer peripheral surface, then balls can be returned to the other end of the screw groove, but the spline nut movement is restricted, leading to increased overall actuator size
Solution Approach 1:
The return tube is nested within the hollow portion of the screw shaft, utilizing the existing internal space for ball return circulation. This eliminates the need for external projections that would increase the actuator's overall volume while maintaining the ball return function.
3Length of moving object
If the spline shaft length is increased to accommodate the return tube projection, then the stroke amount requirement is met, but the electric actuator size increases
Solution Approach 1:
The ball return system transitions from a radial configuration (projecting outward) to an axial configuration (within the hollow portion). This allows the effective ball return path to be achieved without increasing the radial dimensions or overall actuator volume, while the spline shaft length is optimized to provide the required stroke amount without excess.
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 design allows for a downsized electric actuator while maintaining a sufficient stroke amount by eliminating the need for a longer spline shaft, as the ball return path is internal, allowing the spline nut to move freely over the entire length.
Implementation Method 1
A screw groove in which balls roll is helically formed in an outer peripheral surface of the screw shaft
Implementation Method 2
a screw groove in which balls roll is helically formed in an outer peripheral surface of the screw shaft
Implementation Method 3
a ball return path coupling adjacent valley portions of the load-rolling groove so as to form an infinite circulation path corresponding to one loop around the screw shaft
Implementation Method 4
The spline shaft is threadedly engaged with the screw shaft through intermediation of a large number of balls
Data Source
AI summary
A ball-screw spline includes: a screw shaft; a ball-screw nut engaged with the screw shaft via balls; and a spline nut assembled to an outside of the ball-screw nut via balls to reciprocate in an axial direction of the ball-screw nut. The ball-screw nut includes a screw portion and an extended portion formed integrally, with the same outer diameter. The screw portion has an inner peripheral surface including a load-rolling groove forming a load path for the balls together with a ball rolling groove on the screw shaft side; and a ball return path coupling adjacent valley portions of the load-rolling groove to form a circulation path corresponding to one loop around the screw shaft. The ball-screw nut has an outer peripheral surface including a ball rolling groove for the spline nut, the ball rolling groove being formed over a range corresponding to the screw portion and the extended portion.