Ball Screw Nut Groove Structure for Smooth Ball Circulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ball screw devices face issues with smooth circulation of balls due to irregular contact between balls and screw threads, which is exacerbated by the difficulty in forming holding portions at the opening edge of the circulation groove during cutting work.
Innovation Solution
A ball screw device with a nut member featuring a forwarding groove and a circulation groove, where an inclination portion with a non-uniform width is formed at the angular portion of the through hole and axial end surface intersection, allowing for smooth ball circulation by providing a holding portion that guides balls over the screw thread.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the circulation groove is formed by cutting work with a tool inserted from the axial direction, then the manufacturing process is simple, but the holding portion cannot be formed at the opening edge of the circulation groove
Solution Approach 1:
The invention changes the cutting approach from axial insertion to radial insertion. The tool is inserted radially through the lateral surface of the nut member rather than axially from the end face, enabling the formation of both the circulation groove and the holding portion at its opening edge. This dimensional change in tool insertion direction resolves the contradiction between manufacturing simplicity and holding portion formation capability.
2Productivity
If the circulation groove is opened to the screw shaft to allow ball circulation, then balls can return to previous position, but balls are liable to be irregularly brought into contact with the screw thread
Solution Approach 1:
The invention introduces a holding portion as an intermediary structure at the opening edge of the circulation groove. This holding portion acts as a mediator that guides balls smoothly from the circulation groove onto the screw thread, preventing irregular contact. The holding portion includes a guide surface that ensures reliable and smooth ball circulation while maintaining the necessary opening to the screw shaft for ball return.
3Reliability
If the opening width of the circulation groove is made smaller than ball diameter to prevent contact, then ball circulation smoothness improves, but holding portion cannot be formed
Solution Approach 1:
The invention resolves this contradiction by changing the tool insertion direction from axial to radial. This allows the holding portion to be formed at the opening edge of the circulation groove even when the opening width is smaller than the ball diameter. The radial cutting approach enables precise formation of the holding portion structure that maintains both smooth ball circulation and manufacturability.
Data Source
AI summary
Provided is a ball screw device including: a large number of balls; a screw shaft (110) having a rolling groove (111) for the balls, which is formed in a spiral shape in an outer peripheral surface of the screw shaft (110); and a nut member (120) having: a through hole that allows the screw shaft (110) to be inserted through the through hole; and a forwarding groove (210), which is formed in an inner peripheral surface (240) of the through hole, and allows the large number of balls to circulate around a periphery of the screw shaft (110) only one round, the nut member (120) being configured to be threadedly engaged with the screw shaft (110) through intermediation of the large number of balls. The forwarding groove (210) includes: a load rolling groove (121) that faces a part of the rolling groove (111) of the screw shaft (110); and a circulation groove (220), which is formed so as to traverse a screw thread of the screw shaft (110) to connect both ends of the load rolling groove (121) to each other. The forwarding groove (210) is formed so as to be adjacent to an opening edge of the through hole of the nut member (120). An inclination portion (230) is provided at an angular portion (310) at which the inner peripheral surface (240) of the through hole and an axial end surface of the nut member (120) intersect with each other, the inclination portion (230) being formed by cutting out the angular portion (310) so that the inclination portion (230) has a non-uniform width along a circumferential direction of the through hole.