Internal-Deflector Ball Screw Fillet Joint for Higher Rotation Speed
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Solution Overview
Problem
The existing piece type ball screws face breakage of engaging portions due to repeated impact forces from rolling elements, leading to stress concentration and limited permissible rotation speed.
Innovation Solution
A piece type ball screw design featuring a screw shaft with a spiral external thread groove and a nut with a spiral internal thread groove, where the piece member has a return groove and engaging portions that extend in opposite directions, with a fillet-shaped joint portion to reduce stress concentration and enhance strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the piece member is provided with engaging portions to accurately position the piece member with respect to the thread groove, then the positioning accuracy is improved, but the engaging portions may be broken due to fatigue from repeated impact forces
Solution Approach 1:
The joint portion between the piece body and engaging portion is formed with a fillet shape (curved transition) instead of a sharp corner. This curvature eliminates stress concentration points that would otherwise exist at sharp transitions, significantly reducing the likelihood of fatigue-induced breakage while maintaining the engaging portion's positioning function
Solution Approach 2:
The fillet shape is applied specifically at the joint portion where stress concentration occurs, rather than changing the entire geometry. This localized modification targets the critical stress area to improve breakage resistance without affecting the overall positioning accuracy provided by the engaging portions
2Productivity
If the permissible rotation speed is increased to improve productivity, then the output is improved, but the engaging portions are subjected to repeated impact forces that cause breakage
Solution Approach 1:
The fillet-shaped joint portion reduces stress concentration, allowing the engaging portions to withstand the increased repeated impact forces that occur at higher rotation speeds, thereby enabling productivity improvement without sacrificing reliability
Solution Approach 2:
The fillet shape acts as a pre-designed stress relief feature that cushions the impact forces before they can cause damage. This preventive design allows the system to operate at higher speeds where impact forces are more severe, without the engaging portions failing
Data Source
AI summary
A piece type ball screw in a screw shaft with a spiral external thread groove on an outer peripheral surface, a nut which is fitted onto the screw shaft and has a spiral internal thread groove on an inner peripheral surface, a plurality of balls rotatably arranged in a track path formed between the external thread groove and the internal thread groove, and a piece member which is attached to the nut and connects the internal thread grooves to each other. The piece member includes a piece body in which a return groove connecting the internal thread grooves is formed and a pair of engaging portions which are provided on the piece body, extend in opposite directions in a circumferential direction of the nut, and engage with the internal thread groove of the nut. A joint portion between the piece body and the engaging portion has a fillet shape.