Ball Screw Recirculation Groove for Smooth Ball Return

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Solution Overview

Problem

The recirculation trajectory of the recirculation groove in existing ball screws is not designed to allow balls to move smoothly due to discontinuities in the tangential directions between the three-dimensional trajectory and the helical trajectory.

Innovation Solution

The ball screw is designed with a recirculation groove that connects to the helical groove such that the tangential directions are substantially continuous by using a groove cross-sectional trajectory curve and a longitudinal trajectory curve, converted to XYZ coordinates to form a three-dimensional recirculation trajectory.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the recirculation groove is designed using conventional trajectory curves (axial horizontal plane curve and axial cross-sectional curve), then the groove structure is simple to design, but the tangential directions between recirculation trajectory and helical trajectory are discontinuous causing balls to move unevenly

Engineering Contradiction:
Improvesmoothness of ball movementVSAvoidcomplexity of trajectory design
Core Design Contradiction:
Ease of operationVSDevice complexity

Solution Approach 1:

The patent transitions from conventional two-dimensional trajectory design (axial horizontal plane and axial cross-section) to three-dimensional trajectory design by introducing the radial direction as a third dimension. The recirculation trajectory is defined by coordinate values in three directions: axial direction (X), radial direction (R), and circumferential direction (θ), enabling continuous tangential connection between recirculation and helical trajectories for smooth ball movement

Inventive Principle:
Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent changes the design parameters from conventional two-dimensional curves to three-dimensional coordinate values (X, R, θ) that define the recirculation trajectory in space. By specifying coordinate values at multiple points along the trajectory and connecting them smoothly, the patent achieves continuous tangential directions while maintaining design simplicity through systematic parameter definition

Inventive Principle:
Principle #35Parameter changes

2Reliability

If the recirculation trajectory is designed to connect tangentially with the helical trajectory in three dimensions, then smooth ball movement is achieved, but the design and calculation complexity increases

Engineering Contradiction:
Improvecontinuity of ball recirculationVSAvoidcomplexity of trajectory calculation
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

The patent divides the recirculation trajectory into multiple segments defined by discrete coordinate values at different points (e.g., start point, intermediate points, end point). Each segment is calculated independently using the three-dimensional coordinate system, and then connected to form the complete trajectory. This segmentation approach ensures tangential continuity while making the calculation process systematic and manageable

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary calculation and definition of the three-dimensional recirculation trajectory before manufacturing. By pre-calculating the coordinate values (X, R, θ) that ensure tangential continuity with the helical trajectory, the patent eliminates the need for complex real-time adjustments during operation, thereby ensuring reliable and smooth ball recirculation

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentUS20260098573A1Ball screw
Publication Date: 2026.04.09 THK CO LTD
  • US20260098573A1 patent drawing
  • US20260098573A1 patent drawing
  • US20260098573A1 patent drawing

AI summary

Provided is a ball screw where a three-dimensionally formed recirculation trajectory of a recirculation groove can be connected to a helical trajectory in such a manner that the tangential directions thereof are substantially continuous. A ball screw (1) includes: a ball screw shaft (2) including a helical groove (2a); a ball nut (3) including a helical groove; and a plurality of balls (4) placed between the helical groove (2a) of the ball screw shaft (2) and the helical groove of the ball nut (3). The ball nut (3) is provided with a recirculation groove that is connected to one end and the other end of the helical groove of the ball nut (3) to recirculate the balls (4). A recirculation trajectory (8) of the recirculation groove is formed on the basis of a groove cross-sectional trajectory curve representing a trajectory along which the balls (4) are recirculated in a groove cross-section of the ball screw shaft (2), and a longitudinal trajectory curve representing a trajectory along which the balls (4) are recirculated in a virtual plane where a trajectory length ω of the groove cross-sectional trajectory curve is an H-axis and a helical trajectory length Fv(ω) is a V-axis.