Ball Screw Spline Groove Layout for Smaller Robot Actuators
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Solution Overview
Problem
The existing ball screw splines used in industrial robots face limitations in size and weight reduction due to the need to maintain a deeper ball screw groove to prevent screw balls from entering the spline groove at intersections, which restricts the miniaturization and lightening of the system.
Innovation Solution
The ball screw spline design features a shaft with a helical ball screw groove and a straight ball spline groove that intersect, where the ball screw groove is made as deep or deeper than the spline groove, and the screw ball is made smaller in diameter than the spline ball, allowing for different recirculation structures and reduced outside diameters for both the nut and outer race.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ball screw groove is made deeper than the ball spline groove to prevent screw balls from entering the spline groove, then the reliability of the ball screw spline is improved, but the size and weight of the ball screw spline increase
Solution Approach 1:
The invention applies different groove depths at different locations: the ball screw groove is made deeper than the ball spline groove only in the region where they intersect, while other regions maintain standard depths. This localized differentiation prevents screw balls from entering the spline groove at the intersection point without requiring the entire ball screw groove to be deeper, thereby minimizing the increase in size and weight while maintaining reliability.
Solution Approach 2:
Instead of making the ball spline groove deeper to prevent interference (the conventional approach), the invention inverts the approach by making the ball screw groove deeper than the ball spline groove. This reversal effectively prevents screw balls from climbing into the spline groove while allowing spline balls to freely access the ball spline groove, achieving the desired separation function with minimal dimensional increase.
2Reliability
If the ball screw groove is made deeper than the ball spline groove to prevent screw balls from entering the spline groove, then the reliability of the ball screw spline is improved, but the size of the ball screw spline increases
Solution Approach 1:
The deeper groove configuration is applied locally only where the ball screw groove and ball spline groove intersect, rather than increasing the depth of the entire ball screw groove system. This localized approach prevents screw ball misrouting at the critical intersection point while minimizing the overall volume increase of the ball screw spline assembly.
3Reliability
If the screw ball is made greater in diameter than the spline ball due to deeper ball screw groove, then the prevention of ball misrouting is improved, but the size reduction of the ball screw spline is limited
Solution Approach 1:
The invention changes the parameter relationship between screw ball and spline ball diameters. By making the screw ball smaller than the spline ball (contrary to conventional design where screw ball diameter is larger), the invention enables both the nut and outer race to have reduced outside diameters. This parameter reversal, combined with the differential groove depth design, achieves both reliable ball separation and compact dimensions.
Data Source
AI summary
A ball screw spline with reduced size and weight includes: a shaft formed in such a manner that a helical ball screw groove and a straight ball spline groove intersect each other; a ball screw nut having a helical ball screw groove facing the ball screw groove in the shaft, the ball screw nut being configured to allow recirculating a screw ball fitting in the ball screw groove in the shaft; and a ball spline outer race having a straight ball spline groove facing the ball spline groove in the shaft, the ball spline outer race being configured to allow recirculating a spline ball fitting in the ball spline groove in the shaft. The ball screw groove in the shaft is made as deep as or deeper than the ball spline groove in the shaft, and the screw ball is made smaller in diameter than the spline ball.