Ball Screw Nut Pulley Structure for Tooth Tip Accuracy
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Solution Overview
Problem
The existing ball screw nut designs face issues with thermal contraction variations in the pulley part, affecting the accuracy of tooth tips and transmission efficiency due to uneven thickness, which can lead to degradation in meshing with toothed belts.
Innovation Solution
A ball screw nut design with a cylindrical nut part and an integrally molded pulley part, where the restriction part is positioned between the nut and pulley parts in the axial direction to minimize thickness variations, using resin material with metal powder for insert molding to reduce thermal contraction, and featuring a projection and recess configuration for relative rotation restriction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the restriction part is provided at a location where the nut part and the pulley part face each other in the radial direction, then the relative rotation can be restricted, but the thickness of the pulley part becomes uneven, causing variations in thermal contraction and affecting tooth tip accuracy
Solution Approach 1:
The restriction part is repositioned from the radial direction to the axial direction, where the extended portion of the pulley part faces the nut part. This dimensional change allows the restriction function to be achieved without creating uneven thickness in the pulley part, thereby maintaining uniform thermal contraction and tooth tip accuracy while still preventing relative rotation between the nut part and pulley part
2Weight of moving object
If the pulley part is molded using only resin material, then the weight is reduced, but the thermal contraction during molding is large, affecting tooth tip accuracy
Solution Approach 1:
The molding material is changed from pure resin to a composite material containing metal powder dispersed in the resin matrix. This composite material reduces the thermal contraction during molding compared to pure resin, while maintaining the weight reduction benefit. The uniform distribution of metal powder throughout the pulley part ensures uniform thermal contraction and maintains tooth tip accuracy
3Manufacturing precision
If the outer peripheral surface of the nut part and inner peripheral surface of the cylindrical portion do not have circumferential surface over the entire axial range, then the manufacturing is simpler, but the thickness of the pulley part varies, causing variations in thermal contraction
Solution Approach 1:
A circumferential surface is formed on the outer peripheral surface of the nut part and inner peripheral surface of the cylindrical portion over the entire axial range where external teeth are formed. This localized quality enhancement ensures uniform thickness of the pulley part in the critical tooth formation area, resulting in uniform thermal contraction and accurate tooth tips, while the rest of the structure maintains manufacturing simplicity
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 design reduces thermal contraction variations, maintains tooth tip accuracy, and enhances transmission efficiency by preventing relative rotation between the nut and pulley parts, thus improving the overall performance of the ball screw nut.
Implementation Method 1
In the thick portion of the driven pulley, thermal contraction is relatively large during the molding of the driven pulley, while in the thin portion of the driven pulley, the thermal contraction is relatively small during the molding of the driven pulley
Data Source
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AI summary
A ball screw nut (100) includes a nut part (110) and a pulley part (120) integrally molded with the nut part (110) on the outer peripheral side of the nut part (110) and having external teeth (121). The pulley part (120) has a cylindrical portion (122) extending in an axial direction and facing the nut part (110) in a radial direction, and an extended portion (123) extending radially inward from the cylindrical portion (122) and facing the nut part (110) in the axial direction. A restriction part (130) for restricting relative rotation of the nut part (110) and the pulley part (120) is provided between a facing surface (125) of the extended portion (123) facing the nut part (110) and a facing surface (115) of the nut part (110) facing the extended portion (123).