Ball Screw Nut Center of Gravity Balancing via Counterweight
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Solution Overview
Problem
In ball screw mechanisms, the protruding portion on the nut's axial end surface causes uneven rotation and vibration, and existing solutions like thinning machined portions to bring the center of gravity closer to the rotational center line either compromise strength, increase weight, or raise manufacturing costs.
Innovation Solution
The ball screw design incorporates recessed portions formed by pieces fitted into through-holes in the nut's radial direction, combining lighter and heavier materials to balance the center of gravity without thinning machined portions, using synthetic resin or metal pieces to achieve this balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a protruding portion is provided on the nut's axial end surface for the return tube attachment, then the ball return passage can be formed, but the center of gravity deviates from the rotational center line causing uneven rotation and vibration
Solution Approach 1:
The invention introduces a counterbalancing protruding portion on the opposite side of the nut to offset the center of gravity deviation caused by the attachment seat for the return tube. This counterweight approach eliminates the harmful vibration generated by uneven rotation while preserving the ball return passage functionality.
Solution Approach 2:
The invention deliberately introduces asymmetric geometry by adding a counterbalancing protruding portion to compensate for the existing asymmetry caused by the attachment seat. This controlled asymmetry restores rotational balance by repositioning the center of gravity onto the rotational center line.
2Object-generated harmful factors
If thinning machined portions are formed to bring the center of gravity closer to the rotational center line, then vibration is reduced, but the strength of the nut is compromised
Solution Approach 1:
Instead of removing material (thinning) to adjust the center of gravity, the invention adds material in the form of a counterbalancing protruding portion. This approach achieves center of gravity correction while preserving the full structural strength of the nut.
Solution Approach 2:
The invention inverts the conventional approach by adding material rather than removing it to correct the center of gravity position. This inverse method achieves the same vibration reduction effect while maintaining structural integrity.
3Object-generated harmful factors
If thinning machined portions are formed to balance the center of gravity, then uneven rotation is reduced, but manufacturing costs increase
Solution Approach 1:
The counterbalancing protruding portion can be formed using standard manufacturing processes such as casting or forging, which are cost-effective and do not require additional complex machining operations. This approach reduces manufacturing costs compared to thinning machined portions.
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
A ball screw in the present invention includes a nut (1) having a spiral groove formed in an inner peripheral surface; a screw shaft (2) having a spiral groove formed in an outer peripheral surface; balls arranged between a raceway formed by the spiral groove of the nut and the spiral groove of the screw shaft; and a ball return passage for returning the balls from an end point of the raceway to a start point. The nut (1) includes a protruding portion (13) protruding from an axial end surface, and the ball return passage is a recessed portion formed in the inner peripheral surface of the nut. Deviation of the center of gravity of the nut (1) from a rotational center line caused by the protruding portion (13) is made smaller by the configuration of the recessed portion.