Multi-Groove Ball Screw Circulation Path for Shorter Nut Length
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Solution Overview
Problem
In ball screw devices with multi-groove screws, the axial length of the nut member becomes excessively long when trying to maintain a sufficient load path length, making it difficult to downsize the device while maintaining load-bearing performance.
Innovation Solution
The design incorporates a screw shaft with multiple rolling grooves of equal lead, and a nut member with corresponding endless circulation paths that include multiple load and no-load portions, allowing the balls to circulate efficiently while reducing the axial length of the circulation path, thus enabling a compact nut member with sufficient load-bearing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the length of the load path is set to be equal to or larger than about one turn around the screw shaft to maximize the number of load-bearing balls, then the load-bearing performance is improved, but the axial length of the nut member becomes excessively long, making downsizing difficult
Solution Approach 1:
The endless circulation path is segmented into multiple distinct portions: load portions where balls bear load in rolling grooves, no-load portions where balls are transferred between grooves, and return portions where balls return to starting positions. This segmentation allows the circulation path to efficiently utilize space while maintaining sufficient load-bearing capacity through multiple distributed load portions.
Solution Approach 2:
The circulation path is designed to extend in the circumferential direction around the screw shaft rather than solely in the axial direction. By utilizing the circumferential dimension, the patent achieves sufficient load path length without proportionally increasing axial length, enabling compact nut member design while maintaining load-bearing performance.
2Force
If a multi-groove screw with large lead is used to increase rated load and rigidity, then the load-bearing capacity and stiffness are improved, but the axial length of the nut member must be increased to accommodate the circulation path
Solution Approach 1:
The circulation path is divided into multiple load portions corresponding to different rolling grooves, allowing the nut member to accommodate multi-groove screws with large lead while maintaining compact axial dimensions. Each load portion contributes to the overall load-bearing capacity without requiring proportional axial length increase.
Solution Approach 2:
The circulation path utilizes the circumferential direction around the screw shaft to achieve sufficient path length for multi-groove operation. This dimensional approach allows the nut member to work with large-lead multi-groove screws while avoiding excessive axial length increase.
3Force
If the number of rolling grooves is increased to improve rated load, then more balls can bear load simultaneously, but the complexity of the circulation path increases
Solution Approach 1:
The circulation path is systematically segmented into standardized portions (load, no-load, and return portions) that can be replicated for each rolling groove. This modular segmentation simplifies the design and manufacturing of circulation paths for multi-groove screws, reducing complexity despite increased number of grooves.
Solution Approach 2:
The circulation path design incorporates universal features that serve multiple functions: load portions bear load for each groove, no-load portions enable ball transfer between grooves, and return portions facilitate ball circulation. This multi-functionality reduces overall system complexity while supporting multiple rolling grooves.
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 configuration allows for a shorter axial length of the nut member while maintaining a sufficient load path, enabling downsizing without compromising load-bearing performance, and facilitating high-speed operation by balancing the action of balls around the rotation center.
Implementation Method 1
a screw shaft 2 having rolling grooves 20 for balls 4 formed in an outer peripheral surface in a spiral shape
Data Source
AI summary
The ball screw device includes: a screw shaft having an N number (N is an integer equal to or larger than 2) of rolling grooves having the same lead; balls configured to roll in the rolling grooves; and a nut member, which is assembled to the screw shaft through intermediation of the balls, and includes one or a plurality of endless circulation paths configured to circulate the balls around the screw shaft. Each of the endless circulation paths of the nut member includes: an N number of load portions, which are configured to allow the balls to roll thereon while bearing a load, and correspond to the N number of rolling grooves, respectively; and an N number of no-load portions, which each couple adjacent ones of the load portions, and are configured to allow the balls to move between the N number of rolling grooves.