Ball Screw Nut Pulley Structure for Tooth Accuracy in Insert Molding
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Solution Overview
Problem
The existing ball screw nuts with integrally molded pulleys experience variations in thermal contraction due to uneven thickness, affecting the accuracy of tooth tips on the pulley's outer peripheral surface, which can lead to decreased transmission efficiency and meshing issues 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 for relative rotation is positioned between facing surfaces in the axial direction, reducing thickness variations and using insert molding with resin material containing metal powder to minimize thermal contraction, and forming the pulley part on the outer periphery of the nut part to ensure consistent radial thickness and reduced weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the driven pulley is integrally molded on the outer peripheral surface of the ball screw nut with unevenness to restrict relative rotation, then relative rotation between the ball screw nut and driven pulley is restricted, but thermal contraction varies due to thickness variations affecting tooth tip accuracy
Solution Approach 1:
The restriction part is repositioned from the radial direction to the axial direction between the nut part and pulley part. This dimensional change allows the restriction function to be achieved without creating thickness variations in the pulley part, thereby eliminating thermal contraction variations that affect tooth tip accuracy.
Solution Approach 2:
The pulley part is designed with uniform thickness in the radial direction while the restriction part is positioned in the axial direction. This local quality differentiation ensures that the tooth formation area maintains consistent thickness for accurate molding, while the restriction function is achieved through the axial positioning of the restriction part between the nut and pulley.
2Weight of moving object
If the pulley part is molded using only resin material, then the pulley part weight is reduced, but thermal contraction during molding increases affecting tooth tip accuracy
Solution Approach 1:
The pulley part is molded using a composite material consisting of resin material containing metal powder. This composite material reduces thermal contraction during molding compared to pure resin, thereby improving tooth tip accuracy while still maintaining lighter weight compared to solid metal construction.
Solution Approach 2:
The material composition of the pulley part is changed from pure resin to resin containing metal powder. This parameter change in material composition reduces the thermal contraction coefficient, allowing for more accurate tooth tip formation while maintaining the weight advantage over solid metal pulleys.
3Ease of manufacture
If the outer peripheral surface of the nut part and inner peripheral surface of the cylindrical portion do not have circumferential surface over entire axial range, then manufacturing is simpler, but thickness variations in the pulley part increase
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 homogeneity in surface formation ensures uniform thickness distribution in the pulley part, eliminating thickness variations that would cause thermal contraction issues.
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 configuration reduces variations in thermal contraction, maintains accuracy of tooth tips, prevents degradation in meshing efficiency, and allows for integral rotation of the nut and pulley parts, enhancing the transmission of rotational force while reducing the weight of the pulley part.
Implementation Method 1
When the pulley part is formed by insert molding on the outer periphery of the nut part, thermal contraction occurs in the pulley part during the insert molding of the pulley part. In a case where the pulley part is formed by insert molding using the molding material containing the metal powder, the amount of thermal contraction of the pulley part during the insert molding can be made small as compared to a case where the pulley part is formed by insert molding using the molding material containing only the resin material.
Data Source
AI summary
A ball screw nut includes a nut part and a pulley part integrally molded with the nut part on the outer peripheral side of the nut part and having external teeth. The pulley part has a cylindrical portion extending in an axial direction and facing the nut part in a radial direction, and an extended portion extending radially inward from the cylindrical portion and facing the nut part in the axial direction. A restriction part for restricting relative rotation of the nut part and the pulley part is provided between a facing surface of the extended portion facing the nut part and a facing surface of the nut part facing the extended portion.