Ball Screw Contact Angle Optimization for Compound Load Durability
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Solution Overview
Problem
Ball screws used in actuators face reduced durability due to uneven load distribution and increased contact surface pressure when subjected to radial and moment loads, in addition to thrust loads, leading to imbalance and reduced lifespan.
Innovation Solution
A ball screw design with a contact angle between the ball and screw groove set within 20-40° and a groove depth of 35% or less than the outer diameter of the ball, along with bridge members connecting the nut's screw grooves, to enhance load distribution and reduce rotational torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the ball screw is used to support compound loads (thrust, radial, and moment loads), then the structural limitations in actuators are reduced and size is minimized, but the durability is appreciably reduced due to increased contacting surface pressure and uneven load distribution
Solution Approach 1:
The patent optimizes the contact angle parameter to 30 degrees and groove depth to 35% or less of ball outer diameter. These parameter changes enable the ball screw to uniformly distribute compound loads (thrust, radial, and moment loads) across multiple balls, reducing contacting surface pressure and improving durability while maintaining load supporting capacity
Solution Approach 2:
The patent applies different geometric characteristics to different parts of the screw groove. By controlling the groove depth to 35% or less of the ball outer diameter and setting the contact angle at 30 degrees, the groove geometry is optimized locally to ensure uniform load distribution among balls under compound loading conditions
2Strength
If the contact angle is increased and groove depth is increased, then the load supporting capacity is improved, but the rotational torque increases and the size of driving motor increases
Solution Approach 1:
The patent identifies optimal parameter ranges: contact angle of 30 degrees and groove depth of 35% or less of ball outer diameter. Within these parameters, the ball screw achieves adequate load supporting capacity while minimizing rotational torque and driving motor size
Solution Approach 2:
The patent uses groove depth of 35% or less of ball outer diameter, which is sufficient to provide adequate load supporting capacity without excessive groove depth that would increase rotational torque. This partial action approach optimizes the balance between load capacity and torque
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 improves durability by uniformizing ball load distribution, reducing contact surface pressure, and extending the lifespan of the ball screw under compound load conditions, while also minimizing the size of the driving motor and power consumption.
Implementation Method 1
a number of balls rollably contained within a ball rolling passage formed by oppositely arranged screw grooves
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4(a)~4(c)
AI summary
An object of the present invention is to improve the durability of a ball screw under the circumstances in which the radial load and the moment load are applied to it. Ball screw comprising a screw shaft (2) formed on its outer circumferential surface with a helical screw groove (2a), a nut (3) adapted to mate with the screw shaft (2) and formed on its inner circumferential surface with a helical screw groove (3a) corresponding to the screw groove (2a) of the screw shaft (2), a number of balls (4) rollably contained within a ball rolling passage formed by the oppositely arranged screw grooves (2a,3a), and bridge members (5) each formed on its inner circumferential surface with a connecting groove (5a) for connecting the screw grooves (3a) of the nut (3) wherein the contact angle (α) between the ball (4) and the screw groove (2a,3a) is set within a range of 20° to 40°.