Screw Device with Hybrid Ball Roller Grooves for Preloading Control
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Solution Overview
Problem
Existing screw devices face challenges in controlling preloading and machining accuracy, especially when bearing heavy loads in one direction, due to the limited elastic deformation of rollers and the need for high-accuracy finishing of roller rolling grooves.
Innovation Solution
A screw device with a screw shaft featuring both ball and roller rolling grooves, where rollers are parallel-arranged to bear loads in one direction and balls in the opposite direction, facilitated by a shim connecting the ball and roller nuts, allowing for easier preloading and reduced nut length for machining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rollers are used to bear heavy loads in one direction, then the allowable load is increased, but the preloading control becomes difficult due to limited elastic deformation of rollers
Solution Approach 1:
The invention combines both rollers and balls as rolling elements in a single screw device. Rollers are used to bear heavy loads in one direction where they excel, while balls are used to bear loads in the opposite direction where their elastic deformation properties enable effective preloading control. This merging allows the device to simultaneously achieve high allowable load and precise preloading control.
2Strength
If two separate grooves are formed on the nut for rollers and balls, then the device can bear heavy loads in one direction, but the nut becomes longer and machining accuracy of roller rolling grooves deteriorates
Solution Approach 1:
The invention uses the dimensional difference between rollers and balls to their advantage. Rollers are arranged with their axes substantially perpendicular to the axial direction of the screw shaft, while balls are arranged in the axial direction. This dimensional arrangement allows both types of rolling elements to coexist in the same nut without requiring excessive axial length, and enables the roller rolling groove to be machined with sufficient accuracy.
3Adaptability or versatility
If the nut is made longer to accommodate both rollers and balls, then both rolling elements can be arranged, but the roller rolling groove becomes difficult to machine with high accuracy
Solution Approach 1:
The invention applies different local arrangements for rollers and balls within the nut. Rollers are positioned in a specific region with their axes perpendicular to the axial direction, while balls are positioned in another region along the axial direction. This local differentiation allows the nut to accommodate both rolling elements without requiring excessive overall length, thereby maintaining manufacturability of the roller rolling groove.
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 enables controlled preloading and reduces the axial length of the roller nut, improving load distribution and machining ease, making it suitable for heavy loads in one direction while maintaining low loads in the opposite direction.
Implementation Method 1
the rollers have the property of permitting only a small amount of elastic deformation
Implementation Method 2
a ball screw having balls movably deposited between a screw shaft and a nut has been in the actual use... enables reduction of a friction coefficient in rotating the screw shaft relative to the nut
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention provides a screw device which takes a heavy load in one direction along the axis of the screw shaft and only a light load in the opposite direction, the screw device capable of providing ease of control of preloading. The screw device of the present invention has a screw shaft 1 with an outer surface having a ball rolling groove 1a for rolling balls 7 and a roller rolling groove 1b for rolling rollers 6 both spirally formed thereon; a ball nut 4 with an inner surface having a ball rolling groove 4a spirally formed thereon facing the ball rolling groove 1a of the screw shaft 1; a roller nut 5 with an inner surface having a roller rolling groove 5a spirally formed thereon facing the roller rolling groove 1b of the screw shaft 1; a plurality of balls 7 arranged between the screw shaft 1 and the ball nut 4; and a plurality of rollers 6 arranged between the screw shaft 1 and the roller nut 5. The ball nut 4 and the roller nut 5 are connected along an axis of the screw shaft 1.